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Nanotechnology | STUDENT CONFERENCE | nanoTR-Student 2013

STUDENT

CONFERENCE

Editors

Prof.

Dr. Leve

nt TRABZON

Assoc.

Prof.

Dr. Huse

yin K

IZIL

Res. Ass

t. Reyh

an SENGUR

nanoTR-Stu

dent 2013

Abstra

ct B

ook

NanotechnologySTUDENT CONFERENCE

nanoTR-Student 2013

Abstract Book

Editors

Prof. Dr. Levent TRABZON

Assoc. Prof. Dr. Huseyin KIZIL

Res. Asst. Reyhan SENGUR

Organized by ITUnano Research Center and Nanoscience and Nanoengineering Graduate Program

22 October 2013

ISTANBUL

4 5


Nanotechnology STUDENT CONFERENCE

nanoTR-Student 2013

Abstract Book

Editors


Assoc. Prof. Dr. Huseyin KIZIL

Res. Asst. Reyhan SENGUR

Organized by ITUnano Research Center and Nanoscience and Nanoengineering Graduate Program

22 October 2013

ISTANBUL

http://www.nsne.itu.edu.tr

http://www.nano.itu.edu.tr

Nanotechnology STUDENT CONFERENCE – nanoTR-Student 2013

22 October 2013

Remzi Ülker Conference Hall

Maslak / İstanbul

There has been a great interest on nanotechnology in the world in the last two decades due to its disruptive characteristics and effects on the present science and technology. There are several research centers established in Turkey concentrating on nanotechnology and its applications. ITUnano Research Center is a nanotechnology research center in a kind, which is composed of a state of the art clean room facility and satellite labs. Since there have been increased activities in the field of nanotechnology at Istanbul Technical University (ITU), we decided to organize a conference, which gives us a platform for exchanging ideas and interactions through research in order to maximize joint research efforts in the field of nanotechnology.

ITUnano-TR student conference aims at interaction through research and enhances synergy and collaboration among researchers. The main focus is on the nanotechnology in broad sense, but it certainly concentrates on nanofabrication, MEMS, nano-sensors, nanomaterials, bionanotechnology, and nanocharacterization. The conference is different in a sense that the presenter should be a researcher, who has not yet graduated from his/her graduate study so that there would be a great sharing experience for them in their presentation of his/her state of the research results. There will be flash presentations, which give us a concise idea of the research and then the comprehensive discussions will be continued in the poster sessions. The conference starts with a plenary talk by Assoc. Prof. Dr. Mustafa Özgür GÜLER on “Self-Assembled Peptide Nanostructures for Functional Materials” followed by flash presentations.

ITUnano-TR conference is jointly organized by ITUnano Research Center and Nanoscience and Nanoengineering Graduate Programme. I would like to acknowledge the program executive board members; Prof. Dr. Ismail KOYUNCU, Prof. Dr. Nilgun Karatepe YAVUZ, Assoc. Prof. Dr. Huseyin KIZIL (Programme Coordinator), Assoc. Prof. Dr. Esra Ozkan ZAYIM for their great efforts to organize the conference. I also would like to thank students (Reyhan SENGUR, Mumin BALABAN, Emre ALTINAGAC and Muhammed BEKIN) for their enthusiastic efforts at the back-stage of the conference.

We hope you spend very pleasant time and fruitful discussions at ITUnano-TR conference-2013.


Head of Department of Nanoscience and Nanoengineering

Pref

ace

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Oral Presentations

Plenary Speaker - Self-Assembled Peptide Nanostructures for 12 Functional Materials M. Ö. Güler Institute of Materials Science and Nanotechnology, National Nanotechnology Research Center (UNAM), Bilkent University

P1- A New Method For Modifying Surface Morphology: Application 16 of Atomic Force Microscopy on Surface Roughness Measurement O. Güven and M.S. Çelik Mineral Processing Engineering Department, Istanbul Technical University

P2- Carbon Nanotube Synthesis With Different Support Materials 20 and Catalysts F. Gumus, N. Yuca and N. Karatepe Energy Institute, Istanbul Technical University

P3- Cell Separation in Microfluidic Channels 24 M. Zuvin, L. Trabzon and H. Kızıl Nanoscience and Nanoengineering Department, Istanbul Technical University Mechanical Engineering Department, Istanbul Technical University Metallurgical and Materials Engineering Department, Istanbul Technical University

P4- Deposition of Nanocrystallized Amorphous Silicon Thin Films 28 by Magnetron Sputtering E. C. Cengiz, E. S. Kayalı and O. Öztürk Nanoscience and Nanoengineering Department, Istanbul Technical University Material Science and Engineering Department, Gebze Institute of Technology Physics Department, Gebze Institute of Technology

P5- Determination of Nanotoxicological Effects of Silver (Ag0) and 42 Alumınıum (Al0) Nanoparticles on Microbial Community Structure in Activated Sludge E. B. Parlak, D. Y. Koseoglu-Imer, İ. Koyuncu Nanoscience and Nanoengineering Department, Istanbul Technical University Environmental Engineering Department, Istanbul Technical University National Research Center on Membrane Technologies, Istanbul Technical University

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P12- Electrochemical Studies on Pt/C Catalyst for Oxygen 72 Reduction Reaction N. E. Şahin and F. Kadırgan Nanoscience and Nanoengineering Department, Istanbul Technical University Chemistry Department, Istanbul Technical University

P13- Fabrication and Characterization of Nanocomposite Hollow Fiber 76 Membrane with Silver Nanoparticles (AgNP) T.Turken, R.Sengur, I. Koyuncu Department of Environmental Engineering, Istanbul Technical University Department of Nanoscience & Nanoengineering, Istanbul Technical University National Research Center on Membrane Technologies, Istanbul Technical University

P14- Growth and Characterization of Vertically Aligned Mutli-Walled 80 Carbon Nanotubes D. Kavrar, İ. Gürkan, D. Cakiorglu, F. Ç. Cebeci, H. Cebeci Faculty of Aeronautics and Astronautics, Istanbul Technical University Faculty of Engineering and Natural Sciences, Sabanci University Faculty of Chemical and Metallurgy Engineering, Istanbul Technical University

P15- Impact Resistance of Hierarchical Composites Reinforced 84 with Carbon Nanotubes Y. Ateşcan, İ.Gürkan, D. Kavrar and H. Cebeci Aeronautic Engineering Department, Istanbul Technical University Metallurgy and Material Engineering Department, Istanbul Technical University

P16- Investigation of the Effects of Mechanical Forces on Cell Behaviour 88 by Using Microfludics Systems S. Z. Birol, A. S. Yazgan, H. Kızıl, L. Trabzon Nanoscience and Nanoengineering Department, Istanbul Technical University Molecular Biology and Genetics Department, Istanbul Technical University Faculty of Chemical & Metallurgical Engineering, Istanbul Technical University Faculty of Mechanical Engineering, Istanbul Technical University

P17- Magnetic Properties of ZnxNi1-xFe2O4 Nanoparticles: Hopkinson Effect 92 M. Sertkol, Y. Öner Department of Physics, Istanbul Technical University

P6- Development and Testing of Nanofiber Filters for Removal of 46 Volatile Organic Compounds (VOC) in Aircraft Cabins A. Küçüksarı, H. Avcı, A. Kılıç and H. Cebeci Department of Aeronautical & Astronautical, Istanbul Technical University College of Textiles, North Carolina State University Department of Textile Engineering, Istanbul Technical University

P7- Differentiation of Umbilical-Cord Blood Mesenchymal Cells 50 and Scaffold Studies for Vessel Engineering P. H. Omay, M. Zuvin, H. Kizil, L. Trabzon, and H. Bermek Department of Molecular Biology and Genetics, Istanbul Technical University NanoScience & NanoEngineering Programme, Istanbul Technical University Department of Metallurgical and Materials Engineering, Istanbul Technical University Department of Mechanical Engineering, Istanbul Technical University

P8- The Effect of Electrospinning Parameters on PCL Electrospun 54 Nanofiber Mats H.Başkan, A.S.Saraç and H. C. Karakaş Textile Engineering Department, Istanbul Technical University Chemistry Department, Istanbul Technical University

P9-The Effect of Carboxyl and Hydroxyl MWCNTs on Mechanical 58 Properties of Hollow Fiber Membranes R. Sengur, T. Turken and I. Koyuncu Department of Nanoscience and Nanoengineering, Istanbul Technical University Department of Environmental Engineering, Istanbul Technical University National Research Center on Membrane Technologies, Istanbul Technical University

P10- Effect of Catalyst Nature and Its Concentration on the Sol-Gel 62 Derived TiO2 Particles H. B. Jalali, L. Trabzon, M. Balaban, H. Kizil Nanoscience and Nanoengineering Department, Istanbul Technical University

P11- Electrochemical Impedance Spectroscopic Characterization 66 of Bioactive Polypyyrole/Polycaprolactone Nanofibers Z. Guler, P. Erkoc and A. S. Sarac Nanoscience and Nanoengineering Department, Istanbul Technical University Chemistry Department, Istanbul Technical University Polymer Science and Technology, Istanbul Technical University

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P23- The Relationship between Hydrophobicity and Transmittance 112 Properties of Polyolefin/Inorganic Oxide Surfaces E. M. Baba, E. Özen Cansoy and E. Özkan Zayim Nanoscience and Nanoengineering Program, Istanbul Technical University Faculty of Science and Letters, Piri Reis University Physics Department, Istanbul Technical University

P24- Simulation and design of a DEP based LOC device 116 for cancer cell separation Y. Genç, E. Altınağaç, L. Trabzon, and H. Kızıl Nanoscience and Nanoengineering Department, Istanbul Technical University Mechanical Engineering Faculty, Istanbul Technical University Chemical & Metallurgical Engineering Faculty, Istanbul Technical University

P25- Spherical Silica Colloidal Particles: An Experimental Study 120 on the Particle Shape and Size Distribution M. Balaban, L.Trabzon and H. Kizil Department of Nanoscience & Nanoengineering, Istanbul Technical University ITU MEMS - Nano/Microelectromechanical Systems R&D Center, Istanbul Technical University Faculty of Mechanical Engineering, Istanbul Technical University Faculty of Chemical & Metallurgical Engineering, Istanbul Technical University

P26- Synthesis and Analysis of Tungsten Oxide-Based 124 Chromogenic Systems A. Tabatabaei Mohseni, E. Özkan Zayim Nanoscience and Nanoengineering Department, Istanbul Technical University Physics Engineering Department, Istanbul Technical University

P18- MEMS Based Gas Sensors for Detecting Nitrogen Oxide Gas 94 A. Develioğlu, L. Trabzon, H. Kızıl Nanoscience and Nanoengineering Department, Istanbul Technical University

P19- Microfluidic Channel Integrated Planar Peristaltic Pump 98 M. Bekin, H. Kızıl and L.Trabzon Faculty of Mechanical Engineering, Istanbul Technical University ITU-MEMS Microelectromechanic Systems Research and Development Center, Istanbul Technical University ITU-NANO Nanotechnology Research Center, Istanbul Technical University Faculty of Chemical and Metallurgical Engineering, Istanbul Technical University Department of Nanoscience & Nanoengineering, Istanbul Technical University

P20- MO-Optics Lithography for Micro and Nano Fluidics 102 R. Yılmaz, M. Bekın, H. Kızıl and L. Trabzon Faculty of Mechanical Engineering, Istanbul Technical University Department of Nanoscience & Nanoengineering, Istanbul Technical University ITU MEMS - Nano/Microelectromechanical Systems R&D Center, Istanbul Technical University ITUnano – Nanotechnology Research Center, Istanbul Technical University Faculty of Chemical & Metallurgical Engineering, Istanbul Technical University

P21- Polystyrene Particle Manipulating Using AC Dielectrophoresis 106 E. Altınağaç, A. C. Sabuncu, L. Trabzon, A. Beskok, H. Kızıl Department of Nanoscience & Nanoengineering, Istanbul Technical University MEMS-Microelectromechanics Research and Development Center, Istanbul Technical University Faculty of Mechanical Engineering, Istanbul Technical University Department of Aerospace Engineering, Old Dominion University Faculty of Chemical and Metallurgical Engineering, Istanbul Technical University

P22- Powder Silicon Based Negative Electrodes for Lithium Ion Batteries 110 T. Cetinkaya, M. Uysal, M.O. Guler, H. Akbulut Engineering Faculty, Department of Metallurgical & Materials Engineering, Sakarya University

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U nderstanding interactions in assembly mechanisms of biological molecules has become a crucial factor in the design of nanoscale materials. For example, protein structure is defined by information encoded in the individual amino acids. The amino acids are joined

together to form peptides which then fold into complex structures.1 A considerable number of the structural features in proteins consist of α-helix and α-sheet secondary structural components of peptides.2 Synthetic methodologies provide routes for synthesis of peptide sequences that are useful in the formation of one-dimensional nanostructures. Non-peptidic moieties can incorporate novel functionalities into supramolecular systems such as photoswitching units and ligands for recognition events.3-5

Figure 1. Self-assembling peptide amphiphiles form nanofibers.6

We study self-assembling peptidic molecules with various functional groups that assemble to form nanofiber networks under controlled conditions.7 These nanofibers mimic the architecture of natural extracellular matrix components and are ideal to encapsulate and signal cells in three dimensions through self-assembly of a nanostructure network. We were able to synthesize and characterize new molecules to enhance recognition of bioactive signals on the surfaces of nanofibers.6 There has been great interest in materials design with biological signals that can

Self-Assembled Peptide Nanostructures for

Functional Materials

Mustafa Özgür Güler *,1

1 Institute of Materials Science and Nanotechnology, National Nanotechnology

Research Center (UNAM), Bilkent University

AbstractThis lecture illustrates concepts of making materials, which mimic the structure and function of the biological materials through programmed self-assembly of small molecules and their applications in functional materials. The self-assembly mechanism that forms the supramolecular aggregates involves non-covalent interactions such as hydrogen bonds, electrostatic and hydrophobic interactions. Diverse functional groups were incorporated into nanostructures, for example bioactive peptide sequences and metal chelating groups as well as hydrophobic motifs that include alkyl chains, steroid rings, and aromatic systems. The potential impact of these nanostructures on functional materials are discussed.

14 15


*Corresponding author: [email protected](1) Ogston, A. G. Annual Review of Biochemistry 1955, 24, 181.(2) Zanuy, D.; Nussinov, R.; Aleman, C. Physical Biology 2006, 3, S80.(3) Renner, C.; Moroder, L. Chembiochem 2006, 7, 869.(4) Dong, S. L.; Loweneck, M.; Schrader, T. E.; Schreier, W. J.; Zinth, W.; Moroder, L.; Renner, C. Chemistry-a European Journal 2006, 12, 1114.(5) Bredenbeck, J.; Helbing, J.; Kumita, J. R.; Woolley, G. A.; Hamm, P. P Natl Acad Sci USA 2005, 102, 2379.(6) Hartgerink, J. D.; Beniash, E.; Stupp, S. I. Science 2001, 294, 1684.(7) Toksoz, S.; Guler, M. O. Nano Today 2009, 4, 458.(8) Guler, M. O.; Soukasene, S.; Hulvat, J. F.; Stupp, S. I. Nano Lett 2005, 5, 249.(9) Guler, M. O.; Hsu, L.; Soukasene, S.; Harrington, D. A.; Hulvat, J. F.; Stupp, S. I. Biomacromolecules 2006, 7, 1855.(10) Bull, S. R.; Guler, M. O.; Bras, R. E.; Meade, T. J.; Stupp, S. I. Nano Lett 2005, 5, 1.(11) Guler, M. O.; Pokorski, J. K.; Appella, D. H.; Stupp, S. I. Bioconjugate Chem 2005, 16, 501.(12) Guler, M. O.; Stupp, S. I. J Am Chem Soc 2007, 129, 12082.(13) Guler, M. O.; Claussen, R. C.; Stupp, S. I. J Mater Chem 2005, 15, 4507.

induce cellular events important in tissue regeneration. The use of self-assembly is particularly attractive, because it can allow biomolecular scaffold formation in situ by delivering liquids containing self-assembling molecules to a target tissue site. We also studied biotinylated model systems for recognition of biotin by avidin on the periphery of the nanofibers and enhanced recognition of biotin was observed by changing the packing density of molecules in the nanofibers.8 Various molecules containing the cell adhesion epitope RGDS were synthesized with branched architectures for enhanced recognition of biological signals for cellular adhesion.9 The self-assembling molecules were also labeled with gadolinium chelated magnetic resonance active groups for magnetic resonance imaging (MRI).10 Longer relaxation times were observed in the presence of the MRI active material we developed than the commercial MRI contrast agents. In addition, we exploited the nanostructures to present various other non-peptidic functional groups. For example, a peptide nucleic acid sequence on the periphery of the self-assembled supramolecular structures was presented to recognize RNA or DNA oligonucleotides.11 High epitope density on the surface of the self-assembled nanostructures was also exploited for catalysis applications. To investigate this, hydrolysis of esters such as 2, 4-dinitrophenyl acetate in the presence of imidazole functionalized nanofibers was studied.12 Enhancement in the hydrolysis rates was observed with imidazole groups presented on the nanofiber surface compared to imidazole in spherical nanostructures and in solution. In addition to functionalizing the periphery of these nanostructures, we also studied the possibility of encapsulating molecules in the hydrophobic interior of the nanostructures by encapsulating hydrophobic molecules, such as carbon nanotubes and pyrene in order to examine the potential use of these systems in biosensors and drug delivery.13

Acknowledgement. This work is supported by TÜBİTAK and TÜBA.

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T he flotation process has been widely used, for over a century, to separate valuable mineral from gangue based on their differences in natural or induced hydrophobicity [1]. In spite of technological developments in science, the physical and chemical principles underlying flotation process

has not been clearly elucidated [2]. Flotation process is affected by many factors such as pH, type and dosage of reagents. Besides other factors, roughness is of great importance for evaluation of flotation processes. Roughness of particles and/or substrates cannot be eliminated for real-world materials which must be taken into consideration for interpretation of AFM measurements [3].

In this study, a new approach for producing rough materials namely sand blasting was investigated by conducting different feed pressures. The effect of this method on morphology of particles was measured by AFM and correlated with the micro flotation efficiencies carried out with both ground and blasted materials.

Fig 1. The AFM image of ground material

Table-I Roughness parameters measured for ground material

A new method for modifying surface

morphologyApplication of Atomic

Force Microscopy on surface roughness

measurement

O. Güven and M.S. Çelik Mineral Processing

Engineering Department, Istanbul Technical University

Ra (µm) Rsk Rqu

0,426 0,189 1,592

AbstractRecent research studies on particle systems generally focused on the effect of morphological parameters, in particular roughness. In this study, a new method for modifying surface characteristics of materials was studied in terms of morphological characteristics and the effects of these on subsequent enrichment processes. The characterization tests were utilized the AFM method. In this paper, a correlation between the values obtained from AFM method and flotation recoveries is summarized.

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Fig 4. The correlation between flotation recovery (%) values with average roughness (Ra)

The results of flotation studies clearly show that the increase in the hydrophobicity of particles and also the corresponding floatability is proportional to the increase in roughness values.

*Corresponding author: [email protected][1] T.T. Chau, W.J. Bruckard, P.T.L. Koh, A.V. Nguyen, A review of factors that affect contact angle and implications for flotation practice, Advances in Colloid and Interface Science, 150, 106-115 (2009).[2] J. Drelich, Adhesion forces measured between particles and substrates with nano-roughness, Minerals & Metallurgical Processing, 23, 226-232, (2006).

Fig 2. The AFM image of blasted materials at 2 bars

Table-II Roughness parameters measured for blasted materials at 2 bars

Fig 3. The AFM image of blasted materials at 2 bars for three times

Table-III Roughness parameters measured for blasted materials at 2 bars for three times

Ra (µm) Rsk Rqu

0,894 0,202 1,645

Ra (µm) Rsk Rqu

0,680 0,737 1,988

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T he importance of nanotechnology has been increasing as a result of its numerous advantages. Nanotechnology applications can be categorized in three main sections which are high technology materials, biotechnology and electronics [1]. Having extraordinary properties, nanomaterials can

be used in different areas such as biotechnology, sensors, energy storage, drug delivery, chemicals [2, 3].In this study, Fe(NO3)3.9H2O, Co(NO3)2.6H2O were used as catalysts and MgO, SiO2, Al2O3 were used as support materials. As produced CNTs synthesized by CCVD were used to investigate the effect of the catalyst and support material type on the carbon efficiency.

2. Experimental StudiesIron nitrate, cobalt nitrate and Fe-Co binary catalysts were impregnated on MgO and SiO2. Catalyst and support material were separately mixed in ethanol solution by ultrasonic mixer with metal to support material ratios of 5:100, 10:100. In order to prepare a mixture with Al2O3 support material, precipitation method was used. The same procedure was followed to have the solution. CNTs were synthesized over alumina, silica and magnesium oxide supported Fe, Co and Fe-Co binary catalysts at 800°C in 30 minutes.

3. Results and DiscussionBefore investigating all support materials and catalysts, Fe-MgO, Fe-Al2O3, Fe-SiO2 with metal to support ratio of 5:100 were selected and TEM, Raman spectroscopy, TGA were used for characterization in order to decide that the produced materials are CNT. It can be clearly seen that the produced materials are carbon nanotubes and the diameters of CNTs are 1.5-5nm. These observations lead to a conclusion that SWCNTs were synthesized at the temperature of 800°C.

Figure-1: TEM images of CNTs synthesized at 800°C a) Fe-MgO b) Fe-Al2O3 c) Fe-SiO2

Carbon nanotube synthesis with different support materials and

catalysts

Fatih Gumus1*, Neslihan Yuca1 and

Nilgun Karatepe1

1Energy Institute, Istanbul Technical University

AbstractA Carbon nanotubes (CNTs) have been synthesized with different methods since the first observation. In this study, CNTs were synthesized by CCVD and the influence of the support materials on the catalytic activity of metals was investigated. Fe, Co, Fe-Co transition metals were impregnated over alumina (Al2O3), silica (SiO2) and magnesium oxide (MgO). Single walled carbon nanotubes were produced at 800° C, whereas multi walled carbon nanotubes were synthesized at 500° C. The duration of synthesis was 30 minutes for all temperatures and support materials. Thermal gravimetric analysis (TGA), Raman spectroscopy and transmission electron microscopy were used for the characterization.

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Raman spectroscopy is a widely used characterization method to investigate the electronic and phonon properties of CNTs because of its short measuring times. The G-band indicates the degree of graphitization whereas D-band represents the defects in the structure. Another important parameter is RBM band which can be seen only in SWCNTs. Thus, it is possible to distinguish between single and multi-walled carbon nanotubes. . ID/IG defines the quality of the carbon nanotubes. Higher ratios mean that the amorphous content of the sample is higher than the ones which have lower ID/IG ratios. Using different catalysts and support materials, SWCNTs were synthesized

Figure-2: Raman Spectra of the SWCNTs with Fe-MgO, Fe-Al2O3, Fe-SiO2 substrates

and their efficiencies were compared in order to understand which catalyst and support material could be the best choice. It is found that MgO is the best support material for the ratio of 5:100 for all catalysts except cobalt. The interaction between MgO and Fe-Co binary catalyst is better than the other support materials, therefore SWCNTs synthesized with Fe-Co/MgO has the highest carbon efficiency. When the catalysts are compared with each other, cobalt reaches its higher carbon efficiency with the use of SiO2 support material whereas Fe works better with MgO and SiO2.

Figure-3: The comparison between the support materials (catalyst/support material ratio of 5:100)

ConclusionThe present study has shown that SWCNT was synthesized at 800°C using CCVD method and single walled carbon nanotube production was proved with the characterization methods such as TEM, Raman spectroscopy and TGA. Considering Raman spectra, peaks which are unique to SWCNTs were seen and also RBM band was another proof of the existence of SWCNTs. According to TEM analysis, diameters of carbon nanotubes were found around 1.5-5 nm.

*Corresponding author: [email protected][1] Miyazaki, K., Islam, N., “Nanotechnology systems of innovation – An analysis of industry and academic research activities”, Science Direct, , 27, 661-675 (2007)[2] Harris, J. F. P., [Carbon nanotube science: Synthesis, properties and applications], Cambridge University Press (2009)[3] Kroto, H. W., Heath, J. R., O’Brien, S. C., Curl, R., F. and Smalley, R. E., “C-60 Buckminsterfullerene”, Nature, 354 (1985)

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T he word microfluidics simply refers to pass a fluid that has very small volume through a device having channels or cubicles [1]. Microfluidics has been becoming widely used in molecular and cellular biology. Microfluidic chips provide fast and exact diagnosis due to their realibility and controllable

capabilities. Miniaturizing provides us many advantages in diagnostic device such as use of small amount of samples, fast reaction time, and different types of tests in one chip and cheapness [2].

Passive methods without any external forces are the ones which is separating microparticles by means of flow regime. Important parameter is the geometry of design to manipulate particle or cells via fluence of channel geometry on carrier fluid thereby particle or cell as well. A particle in a solution experience drag and lift forces, primarily. Lift forces effect the particle in two ways. One of these effects is shear induced lift force which drags the particles through the wall from the center. Other effect is wall induced lift force which pushes the particle away from the wall to the center [3]. It is observed that with addition of curved shapes to channel geometry, particles experience a secondary force called as Dean force and two opposite directioned vortices are observed at the top and bottom of the channel and they lead particles to move circular through the cross-section path. Balance between lift forces and Dean force make the particles locate in equilibrium positions [4].

Figure-1: Forces acting on a particle in curved channels [5].

Channels which have height x width 81 μm x 400 μm, 84 μm x 500 μm, 91 μm x 600 μm and 86 μm x 700 μm dimensions were fabricated. Channels had one inlet and three outlets. After culturing both MCF7 (~ 20 μm in diameter) and MDA-MB-231 (~ 15 μm in diameter) cells, target cell –MCF7- has stained with fluorescent dye and effectiveness of dye was investigated with flow cytometry. Then, a million labeled MCF7 and a million unlabeled MDA-MB-231 cells were mixed in 100 ml

Cell separation in microfluidic channels

Merve Zuvin,1

Levent Trabzon 2*

and Hüseyin Kızıl 3

1 Nanoscience and Nanoengineering

Department, Istanbul Technical University

2 Mechanical Engineering Department, Istanbul

Technical University 3 Metallurgical and Materials

Engineering Department, Istanbul Technical University

AbstractMicrofabrication has recently found many advanced application areas in. Microfluidics has been becoming widely used in molecular and cellular biology. In this work, Dean force coupled curved microchannels were designed for concentration of MCF7 human breast cancer cells from a suspension that contains MDA-MB-231 and MCF7 human breast cancer cell lines. Cell enrichment possibilities were investigated and shown for different flow rates and channel dimensions.

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PBS solution. 20 ml cell suspension was used for each experiment. It was observed that high flow rates are required for focusing of MCF7 cells. 600 μm wide and 91 μm high channel experiment was performed at 2000 – 2500 – 3000 - 3500 μl/min, respectively and focus positions for each flow rate was investigated with optical microscope images and intensity analysis. Fluorescence intensity analysis was done to show whether there is focus or not. Fig. 2 shows the microscope image and intensity analysis result of focused and MCF7 cells at 3500 μl/min in 600 μm wide channel. According to results MCF7 cells tend to equilibrate in one direction and at 3000 and 3500 μl/min focusing of MCF7 cells were observed.

Figure-2: Focus image and intensity analysis result for 600 µm wide channel

Experiments showed that MCF7 enrichment at the second outlets of each channel and it was confirmed with flow cytometry analysis. Fig. 3 shows the flow cytometry results for each outlet. Acccording to results at 3500 μl/min fluorescent intensity percentages are much higher from at second outlet when three outlets are compared.

Figure-3: Flow cytometry analysis results for 1st, 2nd and 3rd outlets, respectively.

400 to 600 μm wide channels can be used for enrichment purposes at high flow rates while 700 μm channel requires higher flow rates rates contrary to the theoretical calculations. Moreover, the flow cytometer results confirm the findings obtained in enrichment studies so that there is an enhanced enrichment at 2nd outlets of 400 to 600 μm wide channels.

*Corresponding author: [email protected][1] P. G. Gross et al., Journal of the Neurological Sciences 252, 135–43 (2007).[2] L. Pilarski et al., International Conference on MEMS, NANO and Smart Systems (ICMENS’04) (2004).[3] A. Bhagat et al., Lab on a Chip, 9, 2973 - 2980 (2009). [4] D. Di Carlo, Lab on a chip 9, 3038–46 (2009).[5] A. Bhagat et al., Biomed Microdevices, vol. 10. (2009)

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D epletion of fossil fuels makes researchers searching new ways to find alternative resources. Depletion of fossil fuels makes researchers searching new ways to find alternative sources. One of those alternatives is solar cells. Because solar cells are eco-friendly, not having motion parts, working at low

temperatures, having long lifetime and the source is sun which is inexhaustible.

There are several types of solar cells. One of the most important is thin film solar cells. Amorphous silicon becomes forefront, because of its cheapness and applying to flexible surfaces.

Since amorphous silicon has lots of defects named as dangling bonds, efficiency is low. Dangling bonds cause formation of localized states which behave as trap in energy band gap. For preventing this effect, nanocrystallized particles are constituted in amorphous silicon matrix by heating amorphous silicon thin film. By the help of formation of nanocrystalline silicon particles, localized states are eliminated partially. So, nanocrystalline silicon can absorb energy from photons in the region between 1.1-1.7 eV where amorphous silicon shows reduced response. It can be said that this higher absorption effect is related with combined effect of amorphous silicon and nanocrystallized silicon. Because of that, efficiency increases by the help of this effect.

Experimental StudyIn this study, amorphous silicon thin films were deposited on (111) single crystalline silicon wafer by magnetron sputtering which is located in Gebze Institute of Technology, Nanotechnology Research Center. DC and RF power were used during deposition process. In DC power, powder silicon target was used. In RF power, single crystalline silicon wafer was also used as target besides powder silicon. Base pressure was ~2x10-8 mbar. Temperature was kept at 18°C for all samples. Before deposition of silicon on substrates, titanium was deposited with a thickness of 150 Å. After that, silicon deposition was done. Thickness of silicon thin film was 300 Å. Amorphous silicon thin films were characterized and after that nanocrystallized silicon particles are obtained by heating of amorphous silicon thin films at 800°C for 1 hour. Each sample was investigated by XPS for identifying which elements thin fim has and its chemical proportion. XPS was connected to magnetron sputtering system. Because of that after deposition process, samples can be investigated without taking them out from vacuumed ambient. Atomic Force Microscopy (AFM) was used for scanning surface topography, Raman Spectroscopy was done for observing amorphousity and crystallinity of thin film and Scanning Electron Microscopy was done for observing thin film laterally.

ResultsX-Ray Photoelectron Spectroscopy (XPS)XPS characterizations were done for all samples after depositions. The impurities in

Deposition of Nanocrystallized

Amorphous Silicon Thin Films by

Magnetron Sputtering

Elif Ceylan Cengiz 1,2*,

Eyüp Sabri Kayalı 1

and Osman Öztürk 3

1 Nanoscience and Nanoengineering Department, Istanbul Technical University

2 Material Science and Engineering Department, Gebze Institute of Technology,

3 Physics Department, Gebze Institute of Technology

AbstractIn this work, nanocrystallized amorphous silicon thin films were synthesized and it was aimed to apply this to solar cell applications which are accepted as one of the most important alternative for renewable energy sources. In accordance with this purpose, by using DC Magnetron Sputtering and RF Magnetron Sputtering, observations were made comparatively. Primarily, amorphous silicon thin film was obtained and then by the help of X - Ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM), Raman Spectroscopy and Atomic Force Microscopy (AFM) thin film samples were investigated. Behind this, annealing was performed on samples at fixed temperature and certain times and nanocrystallized silicon particles were obtained.

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thin films were observed in some cases and the proportion of them in thin films was calculated by CASA XPS programme.

At first, substrate which is wanted to be used was characterized by XPS for comparison. After that, because every samples were deposited by titanium before deposition of silicon, titanium deposited samples were characterized by XPS.As seen from Figure-1, silicon, carbon, oxygen and their Auger peaks are found in XPS spectrum of native oxidized single crystalline silicon.

Figure-1 : XPS spectrum of native oxidized (111) oriented single crystalline silicon substrate.

Carbon and oxygen are contaminations which are because of keeping substrates in environment, when they were not used. The chemical proportion of native oxidized single crystalline silicon substrate is shown in Table-I.

Table-I Chemical proportion of native oxidized single crystalline silicon substrate.

From Figure-2, titanium deposited silicon surface has titanium and oxygen. The reason of being oxygen at surface is due to oxidation of titanium easily. Even if there is small amount of oxygen in environment, titanium pulls toward oxygen itself. The oxygen content in thin film is 14.3 %.

Figure-2 : XPS spectrum of titanium deposited silicon substrate.

The XPS spectrums belong to 1 Watt, 4 Watt, 10 Watt and 15 Watt can be seen from Figure-3. It can be only seen silicon and its Auger peaks in high resolution XPS spectrum of silicon films. Before silicon deposition, titanium deposition was done on silicon substrate. Titanium peaks do not appear in this spectrum. Thus, it can be said that silicon films were formed for all power ranges. By looking Figure-3, it can be said that all the films have not any impurity such as oxygen.

Figure-3 : XPS spectrum of samples deposited at 1 Watt, 4 Watt, 10 Watt and 15 Watt.

After applying several ranges of power, it was decided that at the lowest and the highest power, which were applied before, the minimum and the maximum argon flow rate were determined. The applied lowest and highest powers were 1 Watt and 15 Watt. In the aspect of such informations, the minimum and the maximum argon flow rates which can form plasma were determined for 1 Watt and 15 Watt. These are 2 sccm and 20 sccm for 1 Watt, 0.8 sccm and 20 sccm for 15 Watt. By the result of these studies, spectrums obtained from XPS are shown in Figure-4.

Figure-4 : XPS spectrum of silicon deposited sample at 1 Watt & 15 Watt and with lowest and highest argon flow rates.

As seen from Figure-4, oxygen content is also observed in all films besides silicon. The oxygen existence is because of argon line that its filter is out of date. The content of oxygen in all films is shown in Table-II.

Table-II The chemical proportion of silicon thin films.

Substrate Silicon (%) Oxygen (%) Carbon (%)

Silicon 53.4 26.7 19.9

Content 1 Watt-2 sccm

1 Watt-20 sccm

15 Watt-0.8 sccm

15 Watt-20 sccm

Silicon (%) 97.3 92.5 97.6 93.8Oxygen (%) 2.7 7.5 2.4 6.2

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After depositions by DC power, depositions by RF power was started to be done. XPS spectrum which belongs to deposition by powder target can be seen from Figure-5.

Figure-5 : XPS spectrum of silicon deposited sample at 10Watt, 15 Watt, 150 Watt and 2.7 argon flow rate.

As seen from Figure-5, silicon films were obtained. But there can be seen argon main peaks resided in 242 eV. The argon content can be because of RF power. In as much as it was not seen in DC power. The argon content in all films is calculated and it is shown in Table-III.

Table III Argon content in silicon thin films.

XPS spectrum which belongs to deposition by substrate target can be seen from Figure-6. There can be seen argon main peaks resided in 242 eV. The argon content can be because of RF power. On the other hand, oxygen which is not seen in samples deposited by powder target is found in thin films.

Figure-6 : XPS spectrum of silicon deposited sample at 10 Watt, 15 Watt, 150 Watt and 2.7 sccm argon flow rate.

It can be seen from Table-IV that when power increases, argon content increases too. It is understood that increase of argon content is related to RF power. Since argon is not seen in samples deposited by DC power.

Table IV Argon and oxygen content of silicon thin films.

After these studies, nanocrystallized amorphous silicon were obtained by heating samples at 800 °C for 1 hour. XPS spectrum of these samples can be seen in Figure-7.

Figure-7 : XPS spectrum of annealed samples deposited by powder and substrate target.

Oxygen content is also seen besides silicon peaks. The oxygen content of films are 2.45 % for powder target and 2.77 % for substrate target.

Raman SpectroscopyThree samples were characterized by Raman Spectroscopy. One of them was deposited by silicon substrate target at 15 Watt and 2.7 sccm with 300 Å. The substrate was native oxidized single crystalline silicon. The Raman spectrum of native oxidized silicon substrate is shown in Figure-8.

Figure-8 : The Raman spectrum of native oxidized silicon substrate.

Power – Argon Flow Rate Argon (%) Silicon (%)

10 Watt-2.7 sccm 4.21 95.79

15 Watt-2.7 sccm 5.24 94.76

150 Watt-2.7 sccm 4.46 95.54

Watt - sccm Argon (%) Oxygen (%) Silicon (%) 15 Watt-20 sccm

10 Watt-2.7 sccm 3.53 1.50 94.97 93.8

15 Watt-2.7 sccm 4.44 1.94 93.62 6.2

150 Watt-2.7 sccm 5.61 1.62 92.70

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The substrate temperature was 18 °C during deposition. Titanium was deposited on silicon substrate with 150 Å thickness before silicon deposition. The Raman spectrum of this sample is shown in Figure-9. As seen from this figure, there are two peaks which are resided in 470 cm-1 and 520 cm-1. A broad band centred at ~470 cm-1 is the typical peak of amorphous silicon and this observation can be related to existence of amorphous silicon in the film [1]. A band peaked at 520 cm-1, which is the characteristic of crystalline silicon, belongs to single crystalline substrate [1, 2].

Figure-9 : The Raman spectrum of the sample deposited by substrate target at 15 Watt and 2.7 sccm argon flow rate.

The other two are annealed samples. Substrates which were used at this time are quartz. This is because it is not wanted that any peak comes from substrate. The Raman spectrum of quartz substrate is shown in Figure-10. As seen from Figure-10, broad peaks are seen in 440 cm-1 and 800 cm-1 which are attributed to SiO2 bonds [3]. And a peak at 488 cm-1 belongs to amorphous silicon. The maximum position of the narrow line corresponds to D1 line and D2 line resided in 605 cm-1 reported in the literature [3, 4]. These lines are assigned to defects in the structure of bulk silica.

Figure-10 : The Raman spectrum of quartz substrate.

One of the quartz samples was deposited by powder target and the other one was deposited by substrate target and each of them was deposited at 15 Watt and 2.7 sccm argon flow rate with 300 Å thickness. Then each of them annealed at 800 °C for 1 hour. They were not deposited with titanium, because high temperature was applied to the samples and at that time titanium and silicon interact with each other. The Raman spectra of annealed samples are shown in Figure-11.

Figure-11 : Raman spectroscopy spectra of silicon deposited and annealed quartz substrates.

As seen from Figure-11, bands peaked at 517 cm-1 and 519 cm-1 which are attributed to the formation of crystalline silicon are observed. In fact, the crystalline silicon peak is observed at 520 cm-1, but depending of annealing temperatures and a slight shift of the 520 cm-1 peak towards lower wavenumbers is observed and it is ascribed to crystalline size and/or stress effects in thin films [1, 2, 5].

Atomic Force Microscopy (AFM)The surface roughness was measured by atomic force microscopy (AFM) (Digital Instruments Veeco Nanoscope IV system). Contact mode was used in these AFM analysis. Before presenting the images which belong to deposited samples, single crystalline silicon substrate and titanium deposited silicon substrate are shown in Figure-12.

Figure-12 : The 10µmx10µm AFM images of samples a) native oxidized single crystalline silicon, b) titanium deposited silicon.

The images shown above represent the single crystalline silicon and titanium deposited silicon which are seen on the Figure-12.a and Figure-12.b, respectively. In the image belongs to single crystalline silicon, there is some conglomeration which are on the top right and down right of the image that is thought to be oxidized

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regions of substrate. This can be because silicon was kept under environment, while substrate was not used.

Figure-13 represents the AFM images of the a-Si:H thin films which show the surfaces of samples deposited at 1 Watt, 4 Watt, 10 Watt and 15 Watt. Root-mean-square (rms) surface roughness of the samples is in the range of 0.655-2.082 nm.

Figure-13 : The 10µmx10µm AFM images of the samples a) 1 Watt, b) 4 Watt, c) 10 Watt and d)15 Watt.

From the AFM images obtained, it is obviously seen that the shape of the grains on the surfaces is spherical. It is thought that these spherical grains are coming from target which is formed of silicon powder. This can be because the silicon powder target is sintered at low temperatures. For surely understanding this effect, deposition at the lowest- the highest powers and argon flow rates were done.

On the other hand, it can be seen from images that while power increases, size of particles broken from target increases too. The particles are arranged in an order in all films, in other words it can be said that films are homogeneous. As at lower power values films are smoother, higher power values films become rougher. Frankly speaking, while at 1 Watt the rms is 0.655 nm, at 4 Watt and 10 Watt the rms are 0.552 nm and 0.663 nm, respectively. At 15 Watt, the rms is 2.082 nm. In other words, it can be said that if power increases, film becomes rougher.

After this study, for understanding of behavior of the particles present on the films, it was decided that the minimum and the maximum argon flow rates were determined according to the maximum and the minimum power. By virtue of this study, it can be understood how the particles form. During this part of the thesis at first 1 Watt and 15

Watt, which are the lowest and highest power used before, were chosen. The maximum argon flow rate giving to the system is 20 sccm. Then the minimum argon flow rates which can form plasma were determined. The minimum argon flow rates are 0.8 sccm for 15 Watt and 2 sccm for 1 Watt. Images for 1 Watt are shown in Figure-14.

Figure-14 : 10µmx10µm AFM images of the samples a) 1 Watt and 2 sccm, b) 1 Watt and 20 sccm.

The images shown in Figure-14 demonstrate the films that 1 Watt and 2 sccm on the left and 1 Watt and 20 sccm on the right. It can be inferred from these images that while argon flow rate increases, the size of particles broken from target increases too. The rms value of 2 sccm is 0.727 nm and the rms value of 20 sccm is 1.783 nm. In other words, while argon flow rate increases, film becomes rougher. This is because target is powder and it is not sintered. It is just pressed. So particles tend to leave easily from target surface, when particles with high energy crash to it. When argon flow rate increases, mean free path of argon particles decreases and collisions increase. So particles reaching to substrate increase, too.

The images of 15 Watt-0.8 sccm and 15 Watt 20 sccm are shown in Figure-15.

Figure-15 : The 2µmx2µm AFM images of the samples a) 15 Watt and 0.8 sccm, b) 15 Watt and 20 sccm argon flow rate.

In Figure-15, it is demonstrated that the films deposited at 15 Watt-0.8 sccm which is on the left and 15 Watt-2 sccm which is on the right. It can be inferred from images that, while argon flow rate increases, the film becomes rougher. The rms value of 0.8 sccm is 0.318 nm and the rms value of 20 sccm is 2.039 nm. As seen from Figure-15, the surface of 15 W-0.8 sccm is very smooth. On the other hand, the surface of 15 Watt-20 sccm is rougher.

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From all these depositions, it can be said that the cleanest surface is obtained from 15 Watt-0.8 sccm argon flow rate. The dirtiest surface is 15 Watt-20 sccm which is understood from rms values.

After these studies, RF power was started to be used. At first, depositions by powder target were done. Figure-16 shows this set.

Figure-16 : The 10µmx10µm AFM images of samples a) 10 Watt and 2.7 sccm, b) 15 Watt and 2.7 sccm, c) 150 Watt and 2.7 sccm.

It can be understood from Figure-16 that while power increases, rms value increase too. The rms values of 10 Watt, 15 Watt and 150 Watt are 0.240 nm, 0.291 nm and 0.396 nm, respectively.

After deposition by powder target, deposition by substrate target was started to be done. The AFM images of samples deposited by substrate target are shown in Figure-17. It can be seen from this image that when power increases, roughness increases too. The rms values of 10 Watt, 15 Watt and 150 Watt are 0.250 nm, 0.345 nm and 3.057 nm, respectively.

If a comparison between powder target and substrate target is made, it can be said that deposition with powder target is faster than substrate target. It can be because powder target is not sintered. By this means, particles are broken easily and deposition rate increases.

Figure-17 : The 5µmx5µm AFM image of sample deposited at a) 10 Watt and 2.7 argon flow rate b) 15 Watt and 2.7 sccm argon flow rate c) 150 Watt and

2.7 sccm argon flow rate.

After these studies, two quartz substrates were deposited by substrate silicon target and powder silicon target. Both of them were annealed at 800 °C for 1 hour. The AFM images of annealed samples are shown in Figure-18.

Figure-18 : The 10µmx10µm AFM image of annealed sample deposited by a) substrate target b) powder target.

By looking Figure-18, it can be said that nanocrystalline silicon particles are obtained. The darker field in image is attributed to the amorphous silicon matrix, while the brighter spherical particles correspond to the crystalline silicon [6]. Spherical nanocrystalline particles were formed by the effect of increasing temperature. Rms roughness of samples is 13.540 nm for substrate target and 10.803 nm for powder target. In the light of these results, it can be said that rms roughness of sample deposited by substrate target is higher than that of powder target. On the other hand, it can be seen from figures that the number of particles formed by powder target is more than the number of particles formed by substrate target. If it is remembered that the AFM images of previous samples which were not annealed, the number of particles fell on samples deposited by powder target are higher than that of substrate target. This is because of particles which are easily broken from powder target.

Scanning Electron Microscopy (SEM)For this system, two samples were chosen from each set and they were broken into two pieces by the help of a diamond pencil. Then, the broken pieces were located to a holder and images were taken from broken parts of the samples. The image can be seen from Figure-19.

Figure 19 : The SEM image of sample which was deposited by DC power, 4 Watt-2.7 sccm.

40 41


As seen from Figure-19 that deposition occured which is understood from color difference. The thickness of coating is 40.9 nm. In fact, the thickness of coating would have been 45 nm, because 15 nm titanium and 30 nm silicon were deposited on the samples. It can be because of the uniformity of plasma in RF power, while in DC it is not.

CONCLUSIONSIn this study, amorphous silicon was deposited by DC and RF power supplies without using hydrogen and nanocrystalline silicon particles can be obtained by annealing samples at 800 ºC for 1 hour. Characterizations were done for every sample. In the light of characterization results, these conclusions are found.

• Magnetron Sputtering can be used for depositing amorphous silicon thin films as well as Plasma Enhanced Chemical Vapor Deposition (PECVD).• RF power is more suitable for depositing amorphous silicon, because film deposited from RF is more homogeneous and cleaner than deposited by DC power.• Films deposited by substrate target are cleaner than deposited by powder target. So it can be said that substrate target is more suitable. In addition, the crystalline formation of thin films deposited by substrate target is higher than powder target as it is understood from Raman Spectroscopy analysis.• When power increases, deposition rate increases, too. But if deposition is slower, quality of thin film becomes much better.• Increasing of argon flow rate causes increasing of deposition rate.

* Corresponding author: [email protected]

REFERENCES[1] Iqbal Z., Veprek S., 1982. Raman scattering from hydrogenated microcrystalline

and amorphous silicon, J. Phys. C, 15 (1982), p. 377.[2] Baghdad R., Benlakehal D., Portier X., Zellama K., Charvet S., Sib J.D., Clin M.,

Chahed L., 2008. Deposition of nanocrystalline Silicon thin films: Effect of total pressure and substrate temperature, Thin Solid Films, 516 (2008) 3965-3970.

[3] Ivanda M., Clasen R., Hornfeck M. and Kiefer W., 2003. Waveguide Raman spectroscopy: a non-destructive tool for the characterization of amorphous thin films, J. Non-Cryst. Solids, 322 46.

[4] Borowicz P., Latek M., Rzodkiewicz W., Laszcz A., Czerwinski A., Ratajczak J., 2012. Deep-ultraviolet Raman investigation of silicon oxide: thin film on silicon substrate versus bulk substrate, Adv. Nat. Sci.: Nanosci. Nanotechnol., 3 (2012) 045003 (7pp).

[5] Saha S.C., Ray S., 1995. Development of highly conductive n-type μc-Si:H films at low power for device applications, J. Appl. Phys., 78 (1995), p. 5713.

[6] Zhao Z.X., Cui R.Q., Meng F.Y., Zhao B.C., Yu H.C., Zhou Z.B., 2004. Nanocrystalline silicon thin films prepared by RF sputtering at low temperature and heterojunction solar cell, Materials Letters, 58 (2004) 3963-3966.

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N anoscience and nanotechnology are dynamically developing fields of scientific interest in the entire world. Nanotechnology is somewhat loosely defined, although in general terms it covers engineered structures, devices, and systems that have a length scale between 1

and 100 nanometers. Nanotechnologies offer potentially huge benefits to society, industry, the environment and health. They can help us improve our quality of life and respond to some of the key issues of the day, such as climate change by cutting greenhouse gas emissions. Other potential benefits include contributions to improved energy storage and efficiency, better diagnosis and treatment of disease, faster computer systems and remediation of polluted air, soil and water.

Nanoparticles may be synthesized from many materials by various physical and chemical methods, with the particles differing in their elemental composition, shape, size, and chemical or physical properties. At nanoscale dimensions,the properties of the material may change significantly to differ completely from their bulk forms. As the size of the material decreases, the proportion of surface atoms increases, which increases the reactivity and makes them highly reactive catalysts with the surface atoms the active centers for elementary catalytic processes. Thus, nanoparticles possess unique electronic, optical, magnetic and mechanical properties that arise explicitly due to their nanometer-scale size. Nanoparticles possess extremely high surface area to volume ratio due to their extremely small size, which renders them highly reactive. High reactivity potentially could lead to toxicity due to harmful interactions of nanoparticles with biological systems and the environment. Nanotoxicology was proposed as a new branch of toxicology to address the gaps in knowledge and to specifically address the adverse effects likely to be caused by nanoparticles. Discipline of nanotoxicology would make an important contribution to the development of a sustainable and safe nanotechnology. Nanotoxicology encompasses the physicochemical determinants, routes of exposure, biodistribution, molecular determinants, genotoxicity, and regulatory aspects. In addition, nanotoxicology is involved in proposing reliable, robust, and data-assured test protocols for nanomaterials in human and environmental risk assessment. Release of nanoparticless to the environment during recycling and disposal is of particular concern for nanoparticles incorporated into limited use and/or disposable products. Once released these nanomaterials would readily undergo transformations via biotic and abiotic processes. Understanding environmental transformations and fate of engineered nanoparticles enable the design and development of environmentally benign nanoparticles. The number of engineered

DETERMINATION OF NANOTOXICOLOGICAL

EFFECTS OF SILVER (Ag0) AND ALUMINIUM

(Al0) NANOPARTICLES ON MICROBIAL

COMMUNITY STRUCTURE IN

ACTIVATED SLUDGE

Elif Buket Parlak1,3,

Derya Y. Koseoglu-Imer3,

İsmail Koyuncu2,3

1Nanobilim ve Nanomühendislik Programı, İstanbul Teknik Üniversitesi

2İnşaat Fakültesi, Çevre Mühendisliği Bölümü, İstanbul Teknik Üniversitesi

3Ulusal Membran Teknolojileri Araştırma Merkezi (MEMTEK),

İstanbul Teknik Üniversitesi

AbstractThis study has focused on identifying the relationship between specific nanoparticles and real activated sludge characteristics. Therefore, this study investigates, by using respiration tests and biological analysis, the inhibitory effect of two different commonly used metal oxide (Ag0 and Al0) nanoparticles on the activity of the microbial communities present in a real wastewater-treatment plant. The experiments were performed at three stages. Firstly, the solubility ratio of nanoparticles was determined at different experimental conditions. Secondly, the effects of nanoparticles were investigated at short-term toxicity tests and respirometric analysis. Finally, the toxicity effects of nanoparticles were determined at long-term tests.

44 45


* Corresponding author: [email protected]

nanoparticles is increasing day-by-day, and it is expected that nanoparticles will be more complex and will have unique chemistries; therefore in order to ensure ‘safe’ nanotechnology, ‘Nanotoxicology’ studies would require a standard set of protocols for its toxicity (including genotoxicity, teratogenecity) and ecotoxicity.

The increased use of nanomaterials introduces the nanoparticles intentionally/unintentionally into the waste streams and wastewater treatment facilities. The impact that wastewater treatment has on nanomaterials, or conversely, the impact that nanoparticles have on wastewater treatment, is largely unknown. Moreover, questions remain on the efficient way to remove these nanoparticles from industrial and domestic wastewater treatment plants. Recent research suggests that some nanoparticles escape from treatment plants and are discharged into natural water bodies. These nanoparticles can remain in the environment for long periods and can be potentially toxic to the aquatic life. Upon release, nanoparticles are likely to interact with aquatic surfaces and biological species as well as aggregate, depending on the interplay between electrostatic and van der Waals interactions. For this reason, there is an urgent need to analyze the possible behavior and fate of nanoparticles in wastewater treatment facilities and wastewater sludge.

This study has focused on identifying the relationship between specific nanoparticles and real activated sludge characteristics. Therefore, this study investigates, by using respiration tests and biological analysis, the inhibitory effect of two different commonly used metal oxide (Ag0 and Al0) nanoparticles on the activity of the microbial communities present in a real wastewater-treatment plant. The experiments were performed at three stages. Firstly, the solubility ratio of nanoparticles was determined at different experimental conditions. Secondly, the effects of nanoparticles were investigated at short-term toxicity tests and respirometric analysis. Finally, the toxicity effects of nanoparticles were determined at long-term tests.

46 47


A ircraft cabins are susceptible of increased VOCs concentration originated from food, beverages, cleaning agents, engine lubricants, oils, hydraulic fluids etc. entrained with ventilation air. Ethanol which is the highest concentration observed in aircrafts is chosen as a target

VOC for this study.

As a photocatalyst, TiO2 is most widely studied for its long-term stability, low cost, and environmental friendliness [1]. TiO2 can be activated under UV light with a wide band gap of (≈3.2 eV) as a catalyst [2].

For filtration systems the filter material requires high surface area for increased efficiency due to increase in interaction between substrate and the catalyst for photocatalytic removal process. By using electrospinning method NFs with high surface area can be produced, and achieved results can be studied by optimizing the parameters. Electrospinning technique has been widely used for manufacturing NFs with different functionalities required in drug delivery systems, nanosensors, micro/nano electronic devices,scaffolds for tissue engineering and filtration media [3,4].

Figure 1: a) A Typical Set-Up of Electrospinning b) Electrospraying Image

In this study, investigation of the efficiency of electrospun NFs with various coating methods of photocatalyst as TiO2 is studied. Figure 1 shows the schematics of electrospinning process and electrospraying method as coating process of TiO2

Development and Testing of Nanofiber

Filters for Removal of Volatile Organic

Compounds (VOC) in Aircraft Cabins

Arda Küçüksarı1,Hüseyin Avcı2,

Ali Kılıç3

Hülya Cebeci1*

1 Department of Aeronautical & Astronautical,

Istanbul Technical University2 College of Textiles,

North Carolina State University, 3 Department of Textile Engineering,

Istanbul Technical University

AbstractNanofibers (NF) which will be used as filters are fabricated by electrospinning and then electrospraying, dip coating and indigenous methods are used for deposition of TiO2 for photocatalytic removal of volatile organic compounds (VOCs) in aircraft cabins. Coating efficiency of the NFs are studied by parameters such as changing fiber properties and the coating methods such as distance of spraying, solution content, temperature and duration time. Characterization studies for the nanofiber filters and TiO2 coated nanofiber filters are performed by scanning electron microscopy (SEM), energy dispersive x- ray spectroscopy (EDS), UV spectroscopy analysis. The testing of the filters for the efficiency of the removal of VOCs are performed using a custom made test system which uses VOC sensors.

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*Corresponding author: [email protected]

REFERENCES[1] Heping Li, Wei Zhang, Siya Huang and Wei Pan, Nanoscale, 4, 801 (2012)[2] A. Wold, Photocatalytic Properties of Titanium Dioxide (TiO2), Chem. Mater. 5

280–283 (1993)[3] Li D and Xia Y, Electrospinning of Nanofibers: Reinventing the Wheel Adv Mater

16:1151–1170 (2004)[4] Burger C, Hsiao B, Chu B, Nanofibrous materials and Their Applications. Annu

Rev Mater Res 36:333–368 (2006)

as an example. Other type of coating methods such as dip coating and indigeneous are being studied for the comparison of different process efficiencies. A commercially available TiO2 (Sigma Aldrich Degussa P25) with 21nm particle size is used and coated onto the electrospun NFs.

Characterizations are performed by SEM (ZEISS Evo Ma 10). Electrospraying SEM results can be seen on the Figure 2 and resulted that with decreasing distance and amount of TiO2 in electrospraying solution provides a better homogenous distribution and less agglomeration of TiO2 on the nanofibers. EDS analyzes are made for the resulted electrospraying process and analyze is shown on Figure 3.

Figure 2: SEM Images of Electrospraying Pictures and EDS Analyzes of of Electrospraying Process

Figure 3: EDS analysis of Electrosprayed Nanofibers

Test results will be performed using a customized test system for the efficiency of VOC removal from the system.

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I n western countries, cardiovascular diseases are the leading cause of mortality. Overall, coronary artery diseases account for more than 54% of the cardiovascular disease-related deaths. Because of problems with current treatment methods such as autografting of arteries or veins, and synthetic grafts, tissue engineering

is a promising approach for treatment of cardiovascular diseases [1,2].

In the current study, umbilical cord blood (UCB) samples collected with informed consent of the mothers. After density-gradient centrifugation, isolated cells were cultured in DMEM-low glucose supplemented with 20% FBS and 1% L-glutamine. Microscobic analyses were done (Figure 1). Anti-CD90/Thy-1, anti-CD34, anti-CD44, anti-CD45 were used for characterization. MSCs obtained from passage 5 were cultured in DMEM-low glucose+10% FBS+1% L-Glutamine with different concentrations of VEGF. Expression of specific endothelial cell (EC) markers such as VCAM-1, KDR/VEGFR2 and VE-Cadherin/CD144 were monitored by flow cytometry.

Figure-1: a. Fibroblastoid and adherent UCB-MSCs (200x, 22nd day), b. UCB-MSC derived ECs (40x, 5th day)

Different geometric designes were performed using L-EDIT (TANİVER TOOLS, USA) (Figure 2).

Figure-2: Designs of different patterns of PDMS (‘p’ means plus-shaped, ‘c’ means circle-shaped, ‘l’ means line-shaped, ‘s’ means square-shaped).

Differentiation of Umbilical-Cord Blood

Mesenchymal Cells and Scaffold Studies for

Vessel Engineering

Pinar Huner Omay,1*

Merve Zuvin,2

Huseyin Kizil,3

Levent Trabzon,4

Hakan Bermek1

1 Istanbul Technical University, Department

of Molecular Biology and Genetics

2 Istanbul Technical University, NanoScience & NanoEngineering Programme

3 Istanbul Technical University, Department of Metallurgical and Materials Engineering4 Istanbul Technical University, Department

of Mechanical Engineering

AbstractIn the current study, the aim is in vitro differentiation of cord blood mesenchymal stem cells (MSC) for new vessel endothelium formation, and understanding of cell behavior on various polydimethylsiloxane (PDMS) scaffolds. Different patterns were designed as plus sign-shaped, circular-shaped, square-shaped and straight line-shaped. One of these patterns was tested for optimization of sterilization. Cell viability/proliferation performance were compared between flat and different patterned PDMS scaffolds.

52 53


*Corresponding author: [email protected][1] J. Gao et al., Journal of Biomedical Materials Research 85A, 1120-1128 (2008). [2] W. J. Zhang et al., J. Cell. Mol. Med. 11(5), 945-957 (2007).

When different concentrations of VEGF were compared, cells treated with 50 ng/ml expressed the highest results for endothelial markers and lowest results for CD44, CD144, CD106, CD309 which were all stem cell markers (Figure 3).

Figure-3: Distribution of expression profiles of different samples.

Plus-shaped PDMS samples were processed by three sterilization procedures: (a) steam autoclave-samples were placed inside an autoclave system at 1210C for 15 min; (b) ultraviolet light (UV)-samples were irradiated with UV light (254 nm, 100μW/cm2 for 30 min) inside a laboratory hood (~50 cm from light source); and (c) ethanol-samples were immersed in 70% ethanol for 30 min. and dried in air at room temperature. Examination of the post-sterilization specimens did not reveal any discernable pattern degradation or surface distortion. ECs were cultured with flat PDMS and different patterns of PDMS scaffolds having different geometric shapes. When different geometric shapes on scaffold were compared, it revealed that “plus-shaped” (p50 and p100) provided high cell viability and proliferation (Figure 4).

Figure-4: MTT analysis of flat PDMS and its different patterns

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N anofibers and nanostructures are promising materials for possible applications in textile industry due to their advantages such as having high surface area to volume ratio, small pore size, low density and high pore volume etc. They can be used in filtration applications, composites as reinforced material, energy

storage, protective clothing, electrical and optical applications, cosmetics and biomedical applications ( wound dressing, tissue template, drug delivery and etc)[1,2].

Electrospinning is an advantageous method for producing nanofibers by using high voltage supplier, a charged polymer jet, needle and a collector. The polymer jet is ejected towards the collector via high electrical field [3,4]. By changing the parameters used different nanofiber diameters can be obtained for different applications.

Figure-1: Mechanism of the electrospinning process [3]

In this study, polycaprolactone, which is a hydrophobic, biodegradable and biocompatible polymer used especially in tissue engineering applications [5,6], is dissolved in THF /DMF solution with volume ratio 50/50 and 80/20. PCL was purchased from Sigma Aldrich and the average moleculer weigth of it is 50,000.

The electrospinning process was carried out in order to have PCL nanofibers. Process paremeters were changed in order to observe the effect of applied voltage, tip-to-collector distance and solution concentration on the diameter and morphological characteristics of these PCL fibers. The voltage is applied between 10-15 kV, the distance from tip-

The Effect of Electrospinning

Parameters on PCL Electrospun

Nanofiber Mats

Havva Başkan,1*

A.Sezai Saraç 2

and Hale Canbaz Karakaş1

1 Istanbul Technical University, Faculty of Textile Technologies and Design, Textile Engineering Department

2 Istanbul Technical University, Faculty of Science and Letters, Chemistry Department

AbstractIn this paper, the effect of electrospinning parameters (solution concentration, applied voltage, solvent composition and distance from tip-to-collector) on polycaprolactone (PCL) nanofiber mats are assessed. The diameter of the fibers are strongly related to the changes in these parameters. PCL pellets are dissolved in the mixture of tetrahydrofuran (THF) and N,N-dimethylformamide (DMF) and electrospinning technique is applied for obtaining nanofibers. While experiencing electrospinning, the variables, namely applied voltage, tip-to-collector distance and solution concentration are changed and nanofiber mats with diameters ranging from about 100 nm to 1µm are achieved. With regard to SEM analysis, it can be said that applied voltage and solution concentration are the most important factors for getting finer nanofiber diameters.

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to-collector is chosen as 10 and 15 cm with respect to 20 wt % and 25 wt % PCL concentration. The flow rate is kept constant at 1 mL/h and the experiment is performed under room temperature.

The resultant nanofibers are observed to have a diameter ranging between 100 nm and 1μm. It has been observed that increasing applied voltage and solution concentration lead to the decrease of the diameter of nanofibers [7,8].

Considering the SEM images it can be concluded that the most homogeneous nanofibers have been obtained with the parameters as 20 wt % concentration, 80/20 THF /DMF volume ratio, 10 kV applied voltage and 15 cm distance between the needle tip and target.

The average diameter is approximately measured as 400 nm, which is reported in the literature as suitable fiber diameter to be used in artificial scaffolds [9]. The obtained nanofibers can be regarded as candidate materials to be used in tissue engineering as an artificial scaffold.

Figure-2: SEM image of optimum PCL electrospun nanofiber

Key Words— polycaprolactone (PCL), electrospinning, nanofibers, process parameters

*Corresponding author: [email protected][1] B. P. Sautter,University of Illinois, Chicago, (2005). [2] S. Ramakrishna, Materials Today 9, No. 3, (2006).[3] M. Rajput, Master Thesis, National Institute of Technology, India (2012).[4] Z.M. Huang et al.,Composites Science and Technology 63, (2003).[5] A. Gholipour Kanani and S. Hajir Bahrami, Journal of Nanomaterials, (2011).[6] C.M. Hsu, Master Thesis, Worcester Polytechnic Institute, (2003).[7] C.M. Hsu and S. Shivkumar, Macromolecular Materials Engineering 289, (2004).[8] K.H.Lee, et al. Polymer 44, (2003).[9] L. Ghasemi-Mobarakeh, et al. Yakhteh Medical Journal 10, No. 3, (2008).

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M embrane separation processes is getting more important for the water and wastewater treatment purposes every day and after 20th century they mostly took over conventional systems. Several types of modules exist and one of them is hollow fiber. Hollow fiber membranes are more

advantageous over flat sheet modules because they have more volume to area ratio which results in more rapid mass transfers such as 30 times faster gas adsorption etc.[1] , are self-supportive, have no waste products, are expensive but cheap when it comes to operational cost, need modest energy requirements, however it can be easily fouled[2]. Phase inversion process is used for their fabrication. Air gap, dope extrusion rate, dope viscosity, coagulation bath temperature, take-up speed, solvent and non-solvent type are main hollow fiber spinning parameters[3] which also make spinning of it so complicated. In recent years, as nanotechnology and nanoparticle usage become widespread, to overcome hollow fiber membrane problem’s (i.e. fouling), researchers made studies about adding nanoparticle to hollow fiber fabrication. However, studies about this subject are not enough.

In our study, we add different types of functional carbon nanotubes for fabricating nanocomposite carbonanotube/ PES hollow fiber membranes. We chose PES because it has good thermal and chemical stability and its easy processability[4]. Carbon nanotubes improve mechanical, thermal stability etc. of materials which is added. The aim of this study is to illustrate how MWCNTs change properties of our hollow fiber membranes. We chose 2 different functional MWCNTS (-OH and –COOH) and spinned 4 different dope concentrations for both functionality. After that we characterized what we fabricated by using both performance related and morphology related characterization methods.

Material & MethodPolyethersulfone (PES) taken from BASF (Ma=72000), the chemical company was used as membrane matrix, polymer. As pore formers, two types of polyvinylprrolidone (PVP) were bought from ISP (US) were used which were PVP-K30 (Ma=65000) and PVP-K90 (Ma=1,500,000). Dimethylformamide (DMF) was used as a solvent bought from Akkim kimya sanayi ve ticaret a.ş. (Turkey). Functionalized multiwalled carbon nanotubes (MWCNTs) were used. Carboxyl multiwalled carbon nanotubes (MWCNT-COOH) were purchased from Timesnano (China) and hydroxyl multiwalled carbon nanotubes (MWCNT-OH) were purchased from Cheaptubes (US).

20% PES, 5% PVP-K30, 2% PVP-K90, 73% DMF was used for pristine dope solution. 0.2%, 0.4%, 0.8% both carboxyl and hydroxyl HF membranes were fabricated (all wt. %). PES, PVP K90 and PVP K30 was dissolved in DMF at 90°C. For MWCNT membranes, MWCNTs were dispersed in DMF by using homogenizator and sonicated. Spinning conditions of hollow fiber system can be seen Table I.

The effect of carboxyl and hydroxyl MWCNTs

on mechanical properties of hollow

fiber membranes

Reyhan Sengur1,3

Turker Turken 2,3

and Ismail Koyuncu 2,3*

1 Department of Nanoscience and Nanoengineering,

Istanbul Technical University2 Department of Environmental Engineering,

Istanbul Technical University3 National Research Center on Membrane

Technologies, Istanbul Technical University

AbstractIn this study, effects of functionalized multiwalled carbon nanotubes (carboxyl and hydroxyl) on the mechanical properties of hollow fiber ultrafiltration membranes were prepared using phase inversion technique were investigated. For this DMA tests were done. SEM images were taken for surface morphology and structural integrity. It was seen that MWCNTs had an effect on the mechanical properties of hollow fiber membranes.

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*Corresponding author: [email protected] [email protected] [1] Pabby, A.K., Sastre, A.M., (2008). Hollow fiber membrane-based separation technology: Performance and design, Book Chapter 4, Taylor & Francis Group, LLC, page 92-135[2]<http://www.cheresources.com/content/articles/separation-technology/hollow-fiber-membranes?pg=3>, date retrieved 30.10.2012[3] Rugbani, A., (2009). Investigating The Influence of Fabrication Parameters on the Diameter and Mechanical Properties of Polysulfone Ultrafiltration Hollow-Fibre Membranes, MSc. Thesis, University of Stellenbosch.[4] Wagner, J., (2001). Membrane Filtration Handbook Practical Tips and Hints by Chem. Eng Second Edition, Revision 2. page 7, 10-13.

Table I: Spinning Conditions

Young’s modulus values were found. SEM images were taken.

ResultsYoung’s modulus data, SEM images of spun membranes and SEM images after DMA testing were given in Fig.1, Fig.2

Fig.1 : Young’s modulus values of spun membranes.

Fig.2 : SEM images of spun membranes.

Parameters ml/min Parameters

Dope soln. velocity 4,62 Air gap(cm) 15

Bore liquid velocity 4,5 Take-up speed (m/s) 0.16

Outer liquid velocity 4,5 Coag. Bath temp. (0C) 50

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I norganic polymerization, beter known as the “sol-gel” process, was discovered in 1846 by Ebelman is an general method for preperating oxides by the wet route at room temperature [1,2]. Organic and inorganic polymerizations both make use of molecular precursors and both are under kinetic control. Their results, therefore,

depend appreciably on the experimental conditions such as catalyst.Several studies have been done about the influence of the catalyst in sol-gel process [3-5]. In synthesis of TiO2 via sol-gel method, hydrolysis and condensation of titaniumtertraisoproxide (TTIP) were occured at room temperature. In this process, the two elementary reactions giving rise to the Ti-O-Ti bond are a hydrolysis reaction followed by a condensation (polymerization) reaction, both requiring a catalyst.

In this study, hydrochloric acid, dimethylformamide (DMF) and ammonia (25%) were used as acid, nucleophile and base catalyst, respectively and the influence of the catalyst nature and its concentration were investigated. The prepared samples were shown in table 1.

Table-I Prepared samples with different catalyst types and concentration

The XRD technique was used to identify the phases of the samples and its patterns are shown in Fig. 1 which confirms anatase structure in H-1, H-2, D-1, D-2, A-1 and amorphous structure in H-3. The amorphous structure of H-2 sample is due to the high concentration of basic catalyst and it is related to the basic hydrolysis and polymerization mechanism and kinetics.

Effect of catalyst nature and its concentration on the sol-gel derived

TiO2 particles

Houman Bahmani Jalali,1,2*

Levent Trabzon 1,

Mumin Balaban1,

Huseyin Kizil11

1 Nanoscience and Nanoengineering

Department, Istanbul Technical University

AbstractTitania powder was synthesized via sol-gel method by hydrolysis and condensation of titaniumtetraisoproxide (TTIP) in isopropanol (IPA) and the effect of the catalyst on the composition and morphology were established. In this process, the two elementary reactions giving rise to the Ti-O-Ti bond are a hydrolysis reaction followed by a condensation (polymerization) reaction, both requiring a catalyst. In this study, hydrochloric acid, dimethylformamide (DMF) and ammonia (25%) were used as acid, nucleophile and base catalyst, respectively. The molar ratio of the catalyst and TTIP was 0.1 and 1. The results show that the composition and morphology of the particles depend on the catalyst nature and its concentration.

Sample Catalyst Catalyst molar ratio

H-1 HCl 0.1

H-2 HCl 1

D-1 DMF 0.1

D-2 DMF 1

A-1 Ammonia 0.1

A-2 Ammonia 1

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* [email protected][1] M. Ebelmann, Ann. Chim. Phys. 1846, 16, 129.[2] M. Ebelmann, C. R. Acad. Sci. Paris 1847, 25, 854.[3] G. Cerveau, R.J.P. Corriu, E. Framery, Polyhedron 2000, 19, 307.[4] G. Cerveau, R.J.P. Corriu, E. Framery, J. Mater. Chem. 2000, 10, 1617.[5] G. Cerveau, R.J.P. Corriu, C. Fischmeister-Lepeytre, J. Mater. Chem. 1999, 9, 1149.

Figure-1: XRD patterns of prepared samples

Samples prepared with DMF have narrower picks than samples prepared with HCl which shows that samples prepared with acidic HCl catalyst have smaller particle size.According to the XRD patterns of H-1 and H-2, by increasing of HCl concentration, it seems that the picks were broader and particle size decreases.

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Biomaterial research has come a long way from bioinert materials, via biocompatible and biodegradable materials to the biomaterials that include bioactivity. Bioactivity can be introduced in polymers via mixing the bioactive molecules and the polymer or via covalent attachment. Large surface area per

unit mass makes nanofibers great candidates for bioactivation, since the loading capacity becomes much higher as compared to on polymer films. Bioactive nanofibers have been prepared by functionalizing electrospun polymer fibers with oligonucleotideds, peptides, drugs or proteins. Polymer nanofibers can be obtained by electrospinning which is a simple and cheap technique that has the potential of large scale production [1].

The bioactive nanofibers have applications in tissue engineering, drug delivery, and biosensors [2, 3]. Biosensors consist of two component; a bioreceptor and a transducer which converts biological signal to an measurable signal such as electrochemical signals [4, 5]. Conductive polymers (CPs), such as polypyrrole (PPy), have been extensively used as transducer in electrochemical biosensors. CPs exhibit interesting and promising electrical properties such as relatively high conductivity and good environmental stability [6]. In this study, bioactive Polypyrrole/Polycaprolactone (PPy/PCL) nanofibers were fabricaticated with DNA functionalization and their characterization were performed by electrochemical impedance spectroscopy (EIS).

PCL nanofibers were fabricated by elecrospinning technique. PPy was polymerized on electrospun PCL nanofibers by in-situ polymerization with Fe3+ as an oxidant and Cl- as a dopant. The calf thymus single-stranded DNA (ssDNA) was immobilized on the PPy coated PCL nanofibers. Surface morphologies of nanofibers were analysed by SEM (Figure 1) and AFM (Figure 2). The structural properties of PCL, PCL-PPy and ssDNA immobilized PCL-PPy nanofibers were investigated by using an FTIR-ATR spectrophotometer (Figure 3). Dynamic mechanical analyses of PCL and PPy/PCL nanofibers were performed (Figure 4) and elastic modulus, thoughness values were evaluated (Table 1). EIS measurements were performed (Figure 3).

According to SEM images the diameters of a PCL nanofiber was 262±52 nm. The surface roughness for PCL nanofibers was 259 nm and for PPy coated PCL nanofibers was 335nm by using AFM Easy Scan software.

Electrochemical Impedance

Spectroscopic Characterization of

Bioactive Polypyyrole/Polycaprolactone

Nanofibers

Zeliha Guler,1*

Pelin Erkoc 2

and A. Sezai Sarac 1,2,3

1 Nanoscience and Nanoengineering Department, Istanbul Technical University,

2 Chemistry Department, Istanbul Technical University,

3 Polymer Science and Technology, Istanbul Technical University

AbstractBioactivity acquired polymers attract great interest due to their advantages in biomedical applications. The bioactive nanofibers have applications in tissue engineering, drug delivery, and biosensors. In this study, bioactive Polypyrrole/Polycaprolactone (PPy/PCL) nanofibers were fabricaticated by DNA functionalization and their characterization were performed in order investigate their potential in biosensor applications.

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at 1800-1500 cm-1 region is a result of vibrations by virtue of the multiple bonds: C=O, C-C, C-N, and NH2 groups and the deformation vibrations of the water molecules (H2O) in DNA [7].

Figure-3: FT-IR-ATR spectra of PCL, PCL-PPy and PCL-PPy-DNA nanofibers.

Figure 4 shows the results of dynamic mechanical analyse of PCL and PCL-PPy mats. The modulus of eleasticity values of plots were found from the slope of a and b curves. Thoughnesses of the samples were calculated from the area under curves with Origin8 Programme integral analysis.

Figure-4: DMA stress-strain curve. (a) PCL (b) PPy coated PCL nanofibers.

PPy coated PCL nanofibers have higher ductility than PCL nanofibers which is approximately 55% strain. Moreover, as it is shown in Table-1 the elastic modulus is

Figure-1: SEM images of PCL (top) and PPy coated PCL (bottom) electropun nanofibers

Figure-2: AFM images of PCL (top) and PPy coated PCL (bottom) electropun nanofibers (topography-left; phase-right).

Specific PCL bands can be seen at 1190, 1727 and 2949cm-1 due to OC–O stretching, carbonyl (C=O) stretching and asymmetric CH2 stretching [6]. PPy has similar carbonyl (C=O) stretching and asymmetric CH2 stretching bands similar with PCL and it has also N-H wagging bands in 1035cm-1. A strong absorption band is detected at 3000cm−1 due to the CH2-stretching vibrations of nucleic acids. The band

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*Corresponding author: [email protected][1] A. Greiner et al.,. Chem., Int. Ed. 46, 5670 (2007).[2] E. Wisse et al., Biomacromolecules 7 (2006).[3] T. G. Kim et al., Biotechn. Progr. 22, 1108 (2006).[4] V. Velusamy et al., Proc. of SPIE, 4, 1 (2009). [5] Kelley, S.O. et al., Nucl. Acids Res., (1999).[6] M. I. Rodríguez et al., IEEE Sensors Journal, 5, 4 (2005). [7] Theophanides, T., Applied Spectroscopy, 35, 5 (1985).[8] Macdonald DD,.Electrochim.Acta 5 (2006).[9] Chang, B.Y., et al., Annual Review of Analytical Chemistry (2010).

found as 0,0620 for PCL nanofibers whereas it is 0,2741 for PPy coated PCL nanofibers that means PPy increased the rigidity of material. It can also be comprehended that toughness is reduced after coating PCL with PPy as a consequence of the reduction the area under the curve.

Table-I Equivalent circuit components for simulating the impedance spectra

Electrochemical impedance spectroscopy and equivalent circuit modelling were performed to evaluate the capacity of the PPy coatings on PCL which is a biodegredable polymer. EIS results showed that PPy coating provided conductivity to PCL electrospun nanofibers. When ssDNA was immobilized on fiber mat, it was seen that the conductivity was slightly increased.

Figure-3. Equivalent circuit modeling of DNA immobilized PCL-PPy. Nyquist (a), Bode phase (b), Bode magnitude (c) and Admittance (d) plots of PCL-

PPy-DNA nanofibers.

PPy coated PCL nanofiber mat exhibited nearly ideal capacitor feature. This is a promising structure which can be used for electrochemical DNA biosensor applications with the further optimizations.

PCL PCL/PPy

Elastic modulus (N/m2) 0.0620 0.2741

Thoughness (J/m3) 70.675 9.831

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F uel cells are electrochemical devices converting the chemical energy of the reactants directly into electrical energy with high efficiency as long as they are supplied with fuel. In order to achieve a high power application, the mechanism of the electrochemical reactions and the electrode kinetics has been the main

research interest over several decades [1-3]. Platinum catalyst on high surface area Carbon is the most widely used electrocatalyst in low temperature fuel cells for cathode and anode reactions. Microwave-assisted polyol synthesis method is simple, fast, and energy efficient method to use as a general way of preparation for supported metal or alloy catalysts [4].

The goal of this study is to determine the electrocatalytic activity and the kinetic parameters of the electrocatalytic reduction of molecular oxygen on synthesized catalyst. There are mainly two pathways for oxygen reduction in acidic media either direct 4-electron reduction or 2-electron reduction pathway in Eq.1 and Eq. 2, respectively. Even for the 2-electron reaction, H2O2 can be further reduced (Eq.3). Also an disproportion reaction may occur (Eq.4), which is generally electrochmically undetectable [5,6]. The desired reaction for a fuel cell cathode is the direct 4-electron pathway due to its high energy conversion and the elimination of possible degradation of the electrode material due to peroxide.

O2 + 4H+ + 4e- ➝ 2H2O Eo =1.299V (Eq.1)

O2 + 2H+ + 2e- ➝ H2O2 Eo = 0.695V (Eq.2)

H2O2 + 2H+ + 2e- ➝ H2O Eo = 1.77V2 (Eq.3)

H2O2 ➝ 2H2O + O2 (Eq.4)

Table-I Kinetic parameters of the oxygen reduction reaction as to Pt/C.

The electrocatalytic reduction of molecular oxygen was carried out by using rotating disk electrode (RDE) with different electrode rotation rates, that is 400, 900, 1600 and 2500 revolution per minute (rpm). Electrochemical results of oxygen reduction were indicated higher current density for Pt/C catalyst as compared to the commercial

Electrochemical Studies on Pt/C Catalyst for Oxygen Reduction

Reaction

Nihat Ege Şahin, 1*

and Figen Kadırgan 2


2 Chemistry Department, Istanbul Technical University

AbstractThe main goal of this study is to determine the electrocatalytic activity and the kinetic parameters of the electrocatalytic reduction of molecular oxygen on carbon supported platinum catalyst, which was synthesized by using microwave assisted method with 2.5 nm. Electrochemical rotating disk electrode (RDE) experiments were conducted in a thermostated standart three-compartment electrochemical cell at 20ºC in 0.1M HClO4. Koutecky-Levich analysis made possible to evaluate the kinetic parameters (kinetic current density (jk), exchange current density (jo), tafel slopes (b), and reaction order). Structural and physical characterizations of the electrocatalyst in question were analyzed by using high resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD) and thermal gravimetric analysis (TGA).

Catalyst EAS m2/g

jk mA/cm2 @0.75V

Tafel Slope mV/dec

jo mA/cm2 TEM d (nm) XRD Mean crys-tallite size / nm

Pt/C 21.37 3.85 115 3.8x 10-4 2.20 2.40

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*Corresponding author: [email protected][1] A. Damjanovic et al., Electrochimica Acta 12, 615, (1967).[2] R. Benitez, A.M. Chaparro, L. Daza, J. Power Sources, 151, 2, (2005).[3] B.E. Conway et al., Int J Hydrogen Energy 12, 607, (1987).[4] N.A. Anastasijevic, et al., J Electroanal Chem 229, 305, (1987).[5] N.M. Markovic, P.N. Ross, Journal Surf. Science Rep. 45, 117, (2002). [6] M.K. Jeon, Y. Zhang, P.J. McGinn, Electrochim Acta, 55, 5318, (2010).

ones and allowed directly four-electron charge transfer reaction for molecular oxygen reduction to water.

Figure-1: Polarization curves on Pt/C electrocatalyst at different rotation rates in O2 saturated 0.1M HClO4 recorded at 5 mVs-1 and 20ºC.

Figure-2: Koutecky-Levich plots with fitting results of Pt/C catalyst for oygen reduction in oxygen saturated 0.1 M HClO4 at various disk potentials.

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I n recent years, membrane processes has widely used for the treatment of drinking water [1], for the treatment of various industrial [2, 3] and municipal wastewaters [4] and it has been accepted as an alternative to conventional processes. Hollow fiber membranes have become prevalent in the field of water and wastewater treatment.

Advantages over flat-sheet membranes include the high mechanical strength and a self-supporting structure to enable back-flushing and greater membrane surface area in a given space [5]. The hollow-fiber membranes can be fabricated by using different methods such as the dry–wet spinning or melt spinning. There are three broad categories of phase separation methods according to all reaction mechanism like the evaporation-induced phase separation (EIPS), non-solvent induced phase separation (NIPS), and thermally induced phase separation (TIPS). [5-7]. The fabrication of hollow fiber membranes is still a complex process because it involves the different fabrication parameters (air gap distance, internal coagulant flow rate, pressure applied on the dope solution, temperature, nature of internal and external coagulants, structure and dimensions of the spinneret, fiber take-up speed, dope extrusion rate, dope solution characteristics (like additive and polymer type), etc.) [8]. Moreover, the major problem in the fabrication process is the determination of interaction effects between the fabrication parameters and the composition of dope solution to obtain an optimum hollow fiber membrane.

Material & MethodPolyethersulfone (PES) was taken from BASF chemical company, two different polyvinylprrolidone (PVP-K30 (Mw=65000) and PVP-K90 (Mw=1,500,000)) were purchased from ISP (US). Dimethylformamide (DMF) was purchased from Akkim (Turkey). Silver nanoparticles (particle size<35 nm) were purchased from Nanoamor (USA). Hollow fiber membranes were fabricated via NIPS method. Spinning conditions were given in Table 1.

Fabrication and Characterization of

Nanocomposite Hollow Fiber Membrane with Silver Nanoparticles

(AgNP)

T.Turken *1-**3,

R.Sengur 2-3,

I. Koyuncu 1-2-3

*1Department of Environmental Engineering, Istanbul Technical University

2Department of Nanoscience & Nanoengineering,

Istanbul Technical University**3National Research Center on Membrane

Technologies (MEM-TEK)

AbstractHollow fiber nanocomposite membranes were fabricated at different silver nanoparticle (AgNP) ratio in dope solutions. The membrane fabrication parameters were optimized by changing the air gap heights and take-up speed values. SEM-EDX, contact angle, porosity and filtration experiments were carried out to characterize the morphology and performance of membranes. At high AgNP concentrations, the kinetic conditions of membrane formation changed during the phase inversion process. SEM analysis showed that the addition of AgNP reduced the pore size onto membrane surface. Moreover the finger-like structure formed at the cross section of membranes. SEM-EDX analysis showed the intensity of silver peak (Ag) onto membrane surface increased with the increasing of AgNP ratio. From the contact angle analysis, it was shown that the addition of AgNP had improved the hollow fiber membrane hydrophilicity. The permeability values of nanocomposite membranes were higher than bare membranes. Moreover, the permeability values increased with the increasing of air gap heights while they decreased with the increasing of take-up speed.

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*Corresponding author: [email protected]; [email protected]

REFERENCES[1] V. Uyak, I. Koyuncu, I. Oktem, M. Cakmakcı, I. Toroz, Removal of trihalomethanes

from drinking water by nanofiltration membranes, J. Hazard. Mater., 152 (2008), 789-794.

[2] M. Cakmakci, N. Kayaalp, I. Koyuncu, Desalination of produced water from oil production fields by membrane processes, Desalination, 222 (2008), 176-186.

[3] I. Koyuncu, F. Yalcin, I. Ozturk, Color removal of high strength paper and fermentation industry effluents with membrane technology, Water Science and Technology, 40 (1999), 241-248.

[4] I. Koyuncu, Direct filtration of Procion dye bath wastewaters by nanofiltration membranes: flux and removal characteristics, J. Chem. Technol. Biotechnol., 78 (2003), 1219-1224.

[5] H. Ohya, S. Shikib, H. Kawakami, Fabrication study of polysulfone hollow-fiber microfiltration membranes: Optimal dope viscosity for nucleation and growth, Journal of Membrane Science 326 (2009) 293–302

[6] S. Jain, J. Bellare, A reviewof TIPS and DIPS techniques for membrane manufacture, Indian Chem. Eng. 46 (2004) 155

[7] W. Albrecht, K. Kneifel, Th. Weigel, R. Hilke, R. Just, M. Schossig, K. Ebert, A. Lendlein Preparation of highly asymmetric hollow fiber membranes from poly(ether imide) by a modified dry– wet phase inversion technique using a triple spinneret, Journal of Membrane Science 262 (2005) 69–80

[8] I.M. Wienk 1, F.H.A. Olde Scholtenhuis, Th. van den Boomgaard *, C.A. Smolders, Spinning of hollow fiber ultrafiltration membranes from a polymer blend. Journal of Membrane Science 106 (1995) 233-243

Table I: Spinning Conditions

Permeability, porosity, young’s modulus values were found. SEM images were taken.

Results and DiscussionExperimental results were given in Fig. 1, Fig. 2.

Fig.1 : Young’s modulus values of spun membranes.

Fig.2 : SEM images of hollow fiber membranes

Parameters ml/min Parameters

Dope soln. velocity 4,62 Air gap(cm) 15

Bore liquid velocity 4,5 Take-up speed (m/s) 0.16

Outer liquid velocity 4,5 Coag. Bath temp. (0C) 50

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S ince the discovery of carbon nanotubes (CNTs) in 1991 by Iijima [1], there has been great interest in their application because of perfect hollow cylindrical geometry and superior mechanical strength as CNTs hold substantial promise as nanocontainers for gas storage, and nanopipes for conveying fluid (such

as gas or water) [2]. Carbon nanotubes (CNTs) with their high aspect ratio, high surface area and intrinsic mechanical, electrical and thermal properties are important nanomaterials for nanoscience.

Three dimensional micro and nanoporous structures are widely investigated for various applications since many improvements on the nanotechnology and microfabrication have been achieved. Carbon based micro and nanodevices are being studied and found applications in a diverse fields such as biomedical, aerospace and energy areas. In this study, vertically aligned multi walled carbon nanotubes (VA- MWNT) were synthesized with CVD method to create small dimension pore sized ultra narrow nanoexchangers for nanoparticle and gas transfer through channels.

Chemical vapour deposition (CVD) allows the growth of carbon nanotubes (CNTs) on surfaces covered with a metal catalyst (mostly Fe, Co, Ni),and there has been extensive research on the growth of aligned and patterned CNTs using thermal CVD on various flat substrates such as silicon substrates from Fe/Al2O3 catalyst film deposited by electron beam evaporation as shown in Figure-1 [3,4].

Figure-1: CVD growth of an aligned MWNT forest: catalyst deposition, catalyst reduction and formation of nano-particles, CNT nucleation, and CNT growth [5].

Growth and Characterization of

Vertically Aligned Mutli-Walled Carbon

Nanotubes

Deniz Kavrar1,

İdris Gürkan2,

Dilek Cakiorglu3,

Fevzi Ç. Cebeci3,

Hülya Cebeci2

1 Faculty of Aeronautics and Astronautics, Istanbul Technical University

Faculty of Engineering and Natural Sciences, Sabanci University

3 Faculty of Chemical and Metallurgy Engineering, Istanbul Technical University

AbstractVertically aligned multi walled carbon nanotubes (VA-MWCNTs) were synthesized by thermal chemical vapour deposition (CVD) using ethylene as carbon precursor at sufficent temperature on supported Al2O3/Fe catalyst substrates. VA-MWNTs were fabricated with a controlled fashion in a preferential alignment for creating small dimension pore sized ultra narrow nanoexchangers for nanoparticle and gas transfer through channels as future study. In this study, VA-MWNT characterizations will be investigated with scanning electron microscopy (SEM), raman spectroscopy and transmission electron microscopy (TEM).

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[1] S. Iijima., Nature 354, 56–58 (1991).[2] J. Yoon, C.Q. Ru , A. Mioduchowski, Composites Science andTechnology 65, 1326–1336 (2005).[3] A J Hart, B.O.Boskovic, A.T. H.Chuang, V.B.Golovko,J,Robertson, B.F.G. Johnson, A .H. Slocum, Nanotechnology 17,1397–1403(2006).[4] A.J.Hart Ph,D dissertation,Chap.4, (2006).[5] N.Yamamoto Ph.D dissertation,Chap.4, (2011).[6] A.J. Hart, A.H. Slocum, Journal of Physical Chemistry B, 110, 8250-8257, (2006).

In this study, we present growth of VA-MWNT films and microstructures from a Fe/Al2O3 catalyst film deposited by electron beam evaporation. The CNTs grow rapidly up to 1 mm height when processed in C2H4/H2/Ar for 15 min. at 750 °C [6]. As-grown VA-MWNT would have <5% volume fraction after the growth procedure and the rest is air (~95%).

Figure-2: SEM image of VA-MWNTs

The quality of VA-MWNTs are studied by Raman Spectroscopy. For SWNTs and MWNTs, G/D ratio measured by Raman spectroscopy can be a CNT quality indicator; G/D ratio is the ratio of intensity at G (graphite) band and at D (defect) band. Figure 3 shows the raman spectroscopy results of VA-MWNTs with thermal CVD system described above.

Figure3: Raman spectroscopy measurement of CNTs: as grown (G/D ratio of 1.24)

VA-MWNT structures would have high porosity and high permeability due to their structures with the CNT-CNT spacing between 80-100 nm depending on the catalyst and precursor system coupling. A micro device will be fabricated with this VA-MWNT and the nanoparticle and gas exchange- transfer will be studied with this context. The growth of VA- MWNTs will be either in a continuous fashion as arrays or templated pillars that will help to characterize the effects of morphology on the effieciency of micro device.

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Epoxy-based composite materials are used in aerospace and automobile industry extensively. However, when impact resistance and mechanical strength is needed in an advanced composite, aero-grade epoxies are still not reached to required properties.[1] With the recent developments, CNTs, the most promising class of

nano-fillers, can be incorporated into the epoxies to enhance the mechanical properties[2] Large aspect ratio, specific surface are properties, multi-functionality of CNTs stand a key role in improving the fracture behavior of advanced carbon fiber composites.[3] The factors, such as CNT morphology, dispersion, alignment and interfacial adhesion between CNTs and epoxy matrixes that influences the properties of nanocomposites have been studied in the literature extensively.[4]

In this research, CNTs are used as nano-reinforcing agents in the epoxy matrices to form hierarchical composites for enhancing the impact resistance. The fabricated hierarchical composites will be characterized using SEM, microCT qualitatively and quantitatively. For mechanical testing, the drop weight impact test will be performed for the specification of impact resistance of hierarchical composite.

Materials and FabricationIn scope of this research two types of composites will be produced. For CNT-reinforced carbon fiber composites, two types of nanotubes will be used.• Base Carbon Fiber Composites (BC-FC): Carbon Fiber + Epoxy Resin• CNT-Reinforced Carbon Fiber Composites (CNT-FC):

• Chemical Vapor Deposition (CVD) Grown MWNT Reinforced Carbon Fiber Composites: CNT + CF + Epoxy Resin (MWNT-FC)

• Baytubes MWNT Reinforced Carbon Fiber Composites: CNT + CF + Resin (BNT-FC)

Carbon fiber is a biaxial fabric with [0°90°] directions and the epoxy resin is RTM-6 from Hexcel. CNTs will be used with randomly directions and the weight fractions of the CNTs between 1-3% (Table-I).

Impact Resistance of Hierarchical

Composites Reinforced with Carbon Nanotubes

Yağmur Ateşcan 1,

İdris Gürkan1,

Deniz Kavrar 2

and Hülya Cebeci1*

1 Aeronautic Engineering Department, Istanbul Technical University

2 Metallurgy and Material Engineering Department, Istanbul Technical University

AbstractCarbon nano structures are potentially important and novel components for implementing into existing aerospace structural composites to form hierarchical structures with multi-functional (mechanical, electrical and thermal) property enhancement. In this study, carbon nanotubes are incorporated into an aero-grade epoxy through mechanical mixing and the CNT reinforced polymer is infused to carbon fibers to form hierarchical composite. The use of nanofillers like CNTs to improve the matrix properties has the ability to achieve advanced properties of filler particles at very low weight fractions, especially for impact toughness of carbon fiber composites. Characterization of hierarchical composites are performed by scanning electron microscopy (SEM) and micro computer tomography (microCT). The investigation of impact resistance of hierarchical composites will be performed by drop weight impact test to carbon fiber and hierarchical composites.

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REFERENCES

[1] K. Lau, M. Lu, C. Lam, H. Cheung, F. Sheng, H. Li. Thermal andmechanical properties of single-walled carbon nanotube bundle-reinforced epoxy

nanocomosites: the role of solvent for nanotube dispersion. Composites Science and Technology, 65 (2005) 719-725.

[2] T. Yokozeki, Y. Iwahori, S. Ishiwata, K. Enomoto. Mechanical properties of CFRP laminates manufactured from unidirectional prepregs using CSCNT- dispersed epoxy. Composite: Part A, 38 (2007)2121-2130.

[3] V. Kostopoulos, A. Baltopoulos, P. Karapappas, A. Vavouliotis, A. Paipetis. Impact and after-impact properties of carbon fiber reinforced composites enhanced with multi-wall carbon nanotubes, Composites Science and Technology, 70, 2010.

[4] N. A. Siddiqui, S. U. Khan, P. C. MA, C. Y. Li, J. Kim. Manufacturing and characterization of carbon fibre/epoxy composite prepregs containing carbon nanotubes. Composites: Part A, 42 (2011) 1412-1420.

[5] Standard Test Method For Measuring the Damage Resistance of a Fiber Reinforced Polymer Matrix Composite to a Drop Weight Impact Event, ASTM D7136/D7136M.

Table-I CNT Loading weight fractions

Fabrication method of the CNT reinforced and non-CNT reinforced carbon fiber composites are vacuum infusion (Figure-1a,b).

Figure-1: (a) Vacuum infusion of BFC, (b) Vacuum infusion of CNTFC

Characterization and TestsSEM analysis will help to understand the morphological structure of hierarchical composites if any dispersion related issues seen qualitatively. Besides that Micro CT studies will help to evaluate the quality of samples quantitatively. Drop impact testing will be performed and test specimens were sized according to ASTM 7136 Standard. (Figure-2a) [5]

Figure-2: (a) Size of test (a) mens [1], (b) Test System Test system was specified at related standard (Figure-2b). The weight will be dropped to the center of the specimens.[5] References

CNT TYPE CNT Loading (%wt) Dispersion

MWNT-FC 0.1 √ √

0.2 √ √

0.3 √ √

BNT-FC 0.1 √ √

0.2 √ √

0.3 √ √

88 89


During whole life, living cells are continuously exposed to mechanical stimulations that can arise from both the external environmental and internal physiological conditions. In case of mechanical stimulations depending on the magnitude, cells respond to changes in a variety

of way. Diffusible chemical messengers are groups of external stimuli such as hormones, mediators etc. that are first transmitted to cells by binding to receptors either on the cell surface or within the cytosol. On the other hand, physical stimuli within the body, fluid shear of endothelial cells activate hormone release and intracellular calcium signaling by cation channels of the transient receptor potential class leading to induce rearrangement of the cytoskeleton (Figure 1). The first important step in the understanding of how cell mechanically respond to physical loads is to investigate how these mechanical signals are converted to biological and chemical responses [1, 2].

Figure 1. Schematic representation of mechanotransduction process at different levels. At level 1, continuum tissue mechanics is used to calculate

the stresses and strains effected on the cell. At level 2, a hybrid of continuum and microstructural approaches allow the subcellular components to be modeled as heterogeneous entities. At level 3, molecular mechanics are

employed to determine the molecular deformation through forces cascading down from the cell and tissue levels [2].

Many biological processes, such as growth, differentiation, migration and apoptosis have been shown affected by changes in cell shape and structural intensity [3, 4, 5]. Alterations in the structural and mechanical properties

Investigation of the Effects of Mechanical

Forces on Cell Behaviour by Using

Microfludics Systems

Semra Zuhal BİROL1*

Ayça SAYI YAZGAN2

Hüseyin KIZIL1,3

Levent TRABZON1,4


2 Molecular Biology and Genetics Department, Istanbul Technical University,

3 Faculty of Chemical & Metallurgical Engineering, Istanbul Technical University,

4 Faculty of Mechanical Engineering, Istanbul Technical University

AbstractIt is known that cells can sense not only biochemical signals but also physical factors which play major role in tissue functionality such as mechanical forces. Mechanobiology is the field that these physical factors function basically through mechanotransduction which is a physiologically process that sense the mechanical forces and conversion of these forces into electrical and biochemical signals.

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[1] Kurth et al., Current Opinion in Chemical Biology 16, 400 (2012).[2] Lim et al., Journal of Biomechanics 39, 195 (2006).[3] Chen et al., Science, New Series 276, 1425 (1997).[4] Boudreau and Bissell, Current Opinion in Cell Biology 10, 640 (1998).[5] Schwartz and Ginsberg, Nature Cell Biology 4, E65 (2002).[6] Hou et al., Cellular and Molecular Bioengineering 4, 591 (2011).[7] Wakatsuki et al., Biophysical Journal 79, 2353 (2000).[8] Zahalak et al., Biophysical Journal 79, 2369 (2000).[9] Guck et al., Biophysical Journal 88, 3689 (2005).[10] Bhagat et al., Medical&Biological Engineering&Computing 48, 999 (2010).[11] Weibel and Whitesides, Current Opinion in Chemical Biology 10, 584 (2006).[12] Sinton et al., Microfluidics and Nanofluidics 1, 2 (2004).

can result in the breakdown of these physiological functions and may pos-sibly lead to diseases [2]. In the beginning of disease, cells exhibit biological and functional alterations that causes to abnormalities in their structural and physical characteristics. For example, during metastasis, some cancerous epithelial cells can be invade, migrate and spread easier than their normal counterparts due to more deformability [6]. Therefore, the mechanical prop-erties of certain types of cells may potentially be used to quantitatively reflect the state of their cytoskeletal structure and health that can be useful for pos-sible applications in clinical diagnostics and even therapy of certain types of diseases [7, 8]. Study of these altered structural–functional relationship and the different responses of the diseased cells to mechanical stimulus that provide us to get important insights into the disease pathophysiology [9].

Figure 2. Representation of a microfluidic system for positioning small molecules with subcellular resolution [11].

For fundamental studies and single cell analysis, several experimental tech-niques such as micropipette aspiration, atomic force microscopy (AFM), op-tical stretcher and magnetic/optical tweezers have been used but some of these techniques do not represent the entire cell physical properties, pre-cisely due to laborious sample preparation and difficulties in equipment us-age. Microfluidics has been an attractive alternative for study of cell and mo-lecular mechanics due to its small length scale, reduced sample and reagent volumes and well-developed microfabrication processes (Figure 2) [10, 11]. Most of these microdevices are fabricated either using silicon and glass, or transparent polymer materials such as polydimethylsiloxane (PDMS) that makes them compatible with most imaging systems for analysis of cells. Mi-crofluidic devices enable real-time studies of cellular responses to mechani-cal or chemical stimulus with precise control of the cellular environment. Also, due to the miniaturized designs that reduce reaction and measurement time, throughput is much higher than conventional methodologies [12].

92 93


Spinel ferrites, MFe2O4, are technologically important group of materials due to their enhanced optical, magnetic, and electrical properties. Spinel ferrites have the general formula of AFe2O4 (where A2+:Fe, Co, Ni, Zn, etc.) and unit cell contains 32 oxygen atoms in cubic close packing with 8 tetrahedral (Td) and 16 octahedral (Oh)

occupied sites. By changing type of the divalent cation, it is possible to obtain significantly different physical and magnetic properties in these ferrites [1].

A variety of wet chemical methods (sol–gel, co-precipitation,hydrothermal, microwave combustion, aerosol, etc.) have been developed to produce Ni-Zn nanoparticles. The combustion method involves the autoignition of an aqueous solution containing an oxidizer (the corresponding metal nitrates) and an organic fuel. Organic compounds (e.g. glycine, urea,citric acid, alanine and carbohydrazide) have been mixed directly that of metal nitrates to enhance the efficiency of combustion synthesis. In this work, urea is used as a fuel, precipitating agent and as a resin former with formaldehyde in synthesis reactions. It leads to formation of corresponding nanocrystalline oxides. The main advantage is that necessary heat for synthesis is obtained directly from the reaction in which the metal nitrates act both as oxidants and as cation sources, while the urea (used as organic compound) functions as the fuel.

In this study, we synthesize magnetic nanoparticles of ZnxNi1-xFe2O4 (with x=0, 0.2, 0.4, 0.6) by using microwave combustion method with urea. Magnetic analysis above the room temperature up to 700°C are realized by AC Susceptibility measurements.

Figure 1. A.C. Magnetic Susceptibility of NiFe2O4 sample as a function of temperature.

*Corresponding author: [email protected][1] M. Sertkol, Y. Koseoglu, A. Baykal, H. Kavas, A.Bozkurt,M.S. Toprak, J. Alloys Compd.

486, 325 (2009).[2] HOPKINSON, J. : Proc. R. Soc. London 48 (1890),1.[3] J. Sláma, M. Šoka, A. Grusková, A. Gonzales, V. Jancárik, Jour. of Elec. Eng., VOL. 62,

NO. 4, 2011, 239–243.

(This work was supported in part by TUBITAK ProjectNo:111T779)

Magnetic Properties of ZnxNi1-xFe2O4

Nanoparticles: Hopkinson Effect

M. Sertkol1,

Y. Öner1*

1 Department of Physics, Istanbul Technical University

AbstractWe synthesize magnetic nanoparticles of ZnxNi1-xFe2O4 (with x=0, 0.2, 0.4, 0.6) by using microwave combustion method. The particle sizes of those samples are estimated to be 36, 13, 20, 10 nm respectively based on Debye Scherrer expression. AC Magnetic Susceptibility measurements have been carried out in the temperature range of 0-700ºC. Curie Temperature for each sample is determined from the susceptibility data. A peak is observed in the susceptibility for NiFe2O4 sample, just below the Curie Temperature (Hopkinson Effect). This peak become broaden with increasing Zn substitution. We discussed experimental results within the theoretical models in the literature.

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N Ox (NO2, NO, etc.) are toxic gases that adversely affect human health. These gases are released by combustion facilities, automobiles, and many other exhaust emission systems. In addition, ozone (O3) is produced by the decomposition of NO2 in the presence of sunlight[1,2]. Sensors capable of

detecting low levels of NOx gases have enormous potential for commercial application in the fields of environmental protection and healthcare.

MEMS-based gas sensors fabricated using semiconducting materials have many advantages: they are highly sensitive to toxic gases, they have a short response time, and they have low power consumption. Especially, the synthesis of gas sensing materials by using a sol–gel method is available for miniaturized gas sensors because of a high specific surface area and low-temperature heat treatment.[3,4]

The cross-section of the micro gas sensor and the patterns for the microheater and sensing electrode are schematically illustrated in Fig. 1(a) and (b), respectively.

Figure-1: (a) Schematic cross-section of the co-planar-type micro gas sensor, and (b) patterns of microheater and sensing electrode.

The SnO2–WO3-based sensing material was deposited in the middle of the MEMS device by a sol-gel process. The prepared Sn-sol and W-sol were then mixed and dropped on the sensing electrode by using a microdispenser. Then, the deposited sensing materials were heated at 350–700°C.

MEMS Based Gas Sensors for Detecting

Nitrogen Oxide Gas

Ayşegül Develioğlu,1

Levent Trabzon 1,

Hüseyin Kızıl1


AbstractIn this study, MEMS-based micro gas sensors were prepared by adopting MEMS technology and using sol–gel process.These sensors can be used for application of the air quality system monitoring the otomobile indoor atmosphere. An array of MEMS-based gas sensors was designed to achieve low power consumption and high efficiency. In order to prepare NO2 sensing W-sol was mixed with Sn-sol, which was prepared separately, and then 1–7 wt.% WO3 was added to the mixture. This mixture was then deposited on the MEMS platform, and the platform was heated to a temperature between 350 and 700°C. The XRD patterns showed that SnO2-WO3 crystallization occurred above 500°C. The response of the gas sensor to NO2 gas was examined at various operating temperatures and gas concentrations.

96 97


Figure-4: Response and recovery transients in electrical resistance upon injection of 1-ppm NO2 gas and purge.

Fig. 5 shows the gas sensitivity as a function of NO2 concentration at various atmospheric temperatures. The atmospheric temperature, the temperature of the reaction chamber within which the gas sensor was placed, was controlled and monitored. The gas sensitivity at 30°C was higher than that at any other temperature in the range of 0 to 50°C.

Figure-5: (a) Schematic cross-section of the co-planar-type micro gas sensor, and (b) patterns of microheater and sensing electrode.

The gas sensing mechanism can be explained as follows: as the solid absorbs more electronegative gas, electrons are transferred to the gas, which causes a space-charge layer (or depletion layer) to be formed near the surface where the uncompensated donor ions exist. A Schottky barrier is then formed which the electron have to overcome passing the region. NO2 has a stronger electron affinity than O2. The resistance increases as the amount of NO2 that is absorbed increases. The concentration of NO2 in the air is detected on the basis of this increase in the resistance.

[1] O. Berger, W.J. Fischer, J. Mater. Sci. Mater. Electron. 15 (2004) 463. [2] H. Meixner, J. Gerblinger, U. Lampe, M. Fleischer, Sens. Actuators B 23 (1995) 119.[3] A.Gotz, I.Gracia, C. Cane, E. Lora-tamayo,M.C.Horrillo, J.Getino, C.Garcia,

J.Gutierrez,Sens. Actuators B 44 (1997) 483.[4] S. Shukla, P. Zhang, H.J. Cho, L. Ludwig, S. Seal, Int. J. Hydrogen Energy 33 (2008)470.[5] M.J. Madou, S.R. Morison, Chemical Sensing with Solid State Devices, Academic

Press, Boston, 1989, p. 13. 10, 23 (2013).

Figure-2: Diffraction patterns of WO3 powders with various annealing temperatures.

Fig. 2 shows the XRD patterns for WO3 powders synthesized by the sol–gel process and heat-treated at temperatures of 150, 300, 500, and 700 °C. Here, Ra is the sensor resistance in air and Rg is the sensor resistance in the presence of the injected NOx gas. Fig. 3 shows the variation in the gas sensitivity (Rs) with an operating temperature when 3-ppm NO2 gas was injected. NO2 gas sensitivity depended on the operating temperature, and the maximum sensitivity (37) was recorded at 290–300°C [5].

Figure-3: Gas sensitivity with heater voltage at 3-ppm NO2. Fig. 4 shows the response and recovery transients for electrical resistance upon injection of 1-ppm NO2 gas and purge. The response and recovery were both very fast, and 90% response and recovery occurred within only a few seconds.

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F luid delivery in lab on a chip (LOC) devices is being produced with expensive, bulky instruments. For experimental purposes this devices are adequate but if this procedure wanted to be done for point of care diagnostics this devices is hard to use. Not only easy to use but also inexpensive way had to be chosen for

point of care diagnostics. Delivery is not enough for diagnostics, though. For complete system after delivery separation or enrichment must be done by LOC device. As shown in Figure a and b this system is already integrated wit a LOC device and separation and enrichments can be done with this system.

In this work, the planner peristaltic pump was chosen to be PDMS based due to its advantages for ease to shape and magnetic forces.

Figure: (a) Micro peristaltic pump mechanism and rotating stabled magnetics can be seen on the figure (b) A disposable PDMS micro

peristaltic pump.

Separation and enrichment mechanism is made by particle focusing mechanism. Focusing mechanism in micro channels is controlling with particle Reynolds number. The particle Reynolds number can be seen and calculated on the next calculation.

Rep: Particle Reynolds numberRec: Channel Reynolds numberDh: Channel Hydraulic diameter

Microfluidic channel integrated planar

peristaltic pump

Muhammed Bekin1,2,3

Hüseyin Kızıl2,3,4,5 and Levent Trabzon1,2,3,5


2 ITU-MEMS Microelectromechanic Systems Research and Development Center,

Istanbul Technical University3 ITU-NANO Nanotechnology Research

Center, Istanbul Technical University4 Faculty of Chemical and Metallurgical

Engineering, Istanbul Technical University1 Department of Nanoscience &

Nanoengineering, Istanbul Technical University

AbstractLab on a chip devices are being used widely and efficiently in point of care diagnostics. Delivery of particles can be either expensive or hard to use. We fabricated a disposable and easy to use peristaltic pump in PDMS via soft lithography and observed that integrated channel can be used for enrichment and separation of particles for leading the point of care diagnostics.

Re p = Recd 2

Dh2 =

Umd2

υDh

100 101


*Corresponding author: [email protected][1] E. Asmolov, J. Fluid Mech., 1999, 381, 63 – 87[2] L.Yobas, K.Tang, S. Yong, E.Ong, A Disposable Planar Peristaltic Pump for Lab on a

Chip, 2008

Focusing mechanism can be summaries asIf Rep >1 then the inertial force is active and the particles moves verticallyIf Rep <<1 then the particle drag force is active and the particles can not move to the flow direction and focusing can be accomplished.

Micro peristaltic pump mechanism is working with a rotational disk, which has stable magnets on it. The rotating disc is adjustable, for different flow rates one can change rpm. Steel ball bearings and magnets are making the peristaltic force to deliver the fluid to the end of pump or in LOC device. We first studied only the peristaltic pump without integrated micro channel. The fist prototype was tested with PDMS based micro channel. We observed enrichment and separation with both experiments. The pump characterization is another important problem for peristaltic pump. For focusing particles the micro channel needs exact flow rates, as design requires.

The experimental set up predicted to be done as figure 2-a, from figure 2-b the real experimental set up can be seen done as figure 2-b. We observed 30 to 3142 ul/min flow rate from 2-345 rpms with 4mm 3 steel ball bearings and the characterization results can be seen on graphs.

102 103


T he most important type of cell manipulation is the inertial microfluidics. This method is about channel geometry, particle size and fluid profile. That is the reason why the lithography is very important for particle manipulation. On traditional lithography system, making small patterns is a hard to do process

and only can do with expensive instruments such as e-beam lithography. For traditional lithography (Süss MA6) there are lots of derivatives that one be able to change for making a perfect pattern. The contact type, collimation angle, light type and light intensity are some of them. For being able to choose the perfect solution for making the right patterns at right sizes, lithography simulation GenISys was used. This work is a light manipulation for better patterns and sizes. In the MA6 system, as can be seen on Figure 1, there are two köhler integrators which make the right collimation angle for best pattern.

Figure 1. Köhler integrators

The importance of köhler integrators can be seen on Figure 1. In this figure one can see that using köhler integrator is making light easy to focus where you want. And with choosing the right angle one can make better resolution in traditional lithography. Thus, making better patterns means better cell manipulation as its about geometry of channel. For fluid profile COMSOL Multiphysics was used and the lithography simulations were made with GenISys software.

MO-Optics Lithography for Micro and Nano

Fluidics

Rumeysa YILMAZ2, 4

Muhammed BEKIN*1,3,4

Hüseyin KIZIL2,3,4,5

and Levent TRABZON1,2,3,4


2 Department of Nanoscience & Nanoengineering,

Istanbul Technical University3 ITU MEMS - Nano/Microelectromechanical

Systems R&D Center, Istanbul Technical University

4 ITUnano – Nanotechnology Research Center, Istanbul Technical University

5 Faculty of Chemical & Metallurgical Engineering, Istanbul Technical University

AbstractMicro and nano fluidic chips are used in the manipulation of cells and tissues and in the point of care diagnosis and treatment of diseases. The most important fabrication step for the designed chips involves lithographic patterning of the system. After undergoing a series of fabrication processes, the chips will be produced and will be ready for usage. However, the defects that are likely to occur during the lithography process need to be minimized in order to achieve an error -free fluidic profile and the pattern has to be transferred onto a mask that is free from defects. The COMSOL Multiphysics simulation results indicated in Figure 2. (a) and (b) illustrate the adverse effects of the changes on the fluidic profile of the model.

104 105


*Corresponding author: [email protected][1] Pablo Benítez and Juan C. Miñano, Ultrahigh-numerical-aperture imaging concentrator,

J. Opt. Soc. Am. A, Vol. 14, No. 8, 1997[2] William Cassarly, Nonimaging Optics: Concentration and Illumination in Michael Bass,

Handbook of optics, Third edition, Vol. II, Chapter 39, McGraw Hill (Sponsored by the Optical Society of America), 2010

[3] Advanced mask aligner lithografi: new illumination system, Süss Microtec, Reinhard Voelkel et. al.

[4] GenISys Mask Aligner Simulation. Ünal N., et. al.

Figure 2. (a) expected fluid model (b) real fluid model after lithography

Thus, making better patterns means better cell manipulation as its about geometry of channel. For fluid profile COMSOL Multiphysics was used and the lithography simulations were made with GenISys software.

Finally, by adjusting the collimation angle of the light source, the desired image patterns can be easily transferred onto the masks through manipulated illumination. The GenISys software was used to simulate the lithography process where the type of exposure mode, the collimation angle and the choice of MO-Optics were determined before simulating the model. The simulation results indicated that the changes encountered on the model before were eliminated and the fluidic flow of the model was found to be unchanged.

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A C Dielectrophoresis (DEP) is the movement of dielectric particles in nonuniform electric fields. Bioparticles can be manipulated using DEP in micro-systems provided that suitable conditions are imposed. However, DEP is not the single mechanism in micro-systems, other effects dominate at

different operation conditions, such as, AC Electrophoresis (AC EP), AC Electroosmosis (ACEO), AC Electrothermal Effects (ACET) and Brownian motion [1,2].

The time averaged dielectrophoretic force on the particle is given by [3]:

where ∇⎥Erms⎥2 is the gradient of the root mean square of the electric field, k(w) is the Clausius-Mossotti (CM) factor, a is the diameter of the particle and Re[…] indicates the real part. CM factor, which is a function of particle and fluid properties, determines the direction of the dielectrophoretic force [3].

ACEO and ACET are predominant hydrodynamic forces in ACEK. ACEO occurs when the electric field interacts with the electrical double layer on electrode surfaces in low conductive mediums whereas ACET is caused by temperature gradients induced by Joule heating which increases linearly with the conductivity of the medium. [1,2]

In this project, a lab-on-a-chip (LOC) device, which has a 200 nm Ti interdigitated electrode layer on a glass substrate and a PDMS chamber (3 mm x 3 mm), is fabricated to investigate the effective regions of each transport mechanism. The standart photolithograpy techniques and lift off processes are used in order to obtain the LOC device.

Fluorescent polystyrene microparticles are added to DI water and suspension conductivity is adjusted by adding NaCl (2.5 x 10-4 S/m, 1.35 x 10-2 S/m, 0.125 S/m). Inverted signals between 1kHz - 5 MHz are applied for the observation of the transport mechanism behaviour under the ranging frequencies and conductivies. Pictures are taken at the steady state.

The experimental results in Fig.1 demonstrates that at low frequencies particles are more polarizable than the medium and undergoes positive DEP (pDEP) whereas at high frequencies particles are less polarizable than the medium and experience negative DEP (nDEP) as stated in previous works in this field [4,5,6]. At the given combinations of frequency, medium conductivity and applied voltage, the DEP force can dominate over hydrodynamic forces.

Our results correlates with the previous works [1,2,3,4,7]. Dominant regions of dielectrophoresis among other AC Electrokinetic transport mechanisms are predicted. A simple static micro particle manipulator is fabricated utilizing photo and soft lithography.

Polystyrene Particle Manipulating Using AC

Dielectrophoresis

Emre Altınağaç 1,2*,

Ahmet Can Sabuncu3,

Levent Trabzon 1,2,3,

Ali Beskok4,

Hüseyin Kızıl 1,2,3,5


Istanbul Technical University2 MEMS-Microelectromechanics Research

and Development Center, Istanbul Technical University


4 Department of AerospaceEngineering, Old Dominion University

5 Faculty of Chemical and Metallurgical Engineering, Istanbul Technical University

AbstractRegion of dominance of dielectrophoresis among other AC Electrokinetic transport mechanisms is predicted. A simple static micro particle manipulator is fabricated utilizing photo and soft lithography. Experimental evidence suggests that dielectrophoresis is effective at certain frequency and conductivity windows.

( )[ ]23 Re2 rmsDEP EkaF ∇= ωπ

108 109


*Corresponding author: [email protected][1] J. Oh, R. Hart, J. Capurro & H. Noh, Lab on a Chip 9, 62-78 (2009). [2] J. Wu, IET Nanobiotechnol., 2, 14-27,(2008).[3] N.G. Green, A. Ramos, & H. Morgan. Journal of Electrostatics, 56, 235-254. (2002).[4] B. Cetin, Y. Kang, Z. Wu, & D. Li, Electrophoresis, 30, 766-772 (2009).[5] S.K. Srivastava,J.L. Baylon-Cardiel, B.H. Lapizco-Encinas, & A.R. Minerick, Journal of

Chromatography A, 1218, 1780-1789 (2011).[6] F. Du, M. Baune, A. Kück, & J. Thöming, Separation Science and Technology, 43,

3842-3855. (2008).[7] S. Park, A. Beskok,, Analytical Chemistry, 8, 2832-2841, (2008).

Figure 1: Experimental results for various mediım conductivites and microelectrode designs. Effective pDEP and nDEP regions are presented.

Experimental evidence suggests that dielectrophoresis is effective at certain frequency and conductivity windows. Strong DEP forces were generated by sharp gradients in the electric field resulting from an AC signal being applied to the Ti microelectrodes fabricated on a microscope glass substrate. pDEP and nDEP forces were demonstrated in each solutions with various conductivities. At low frequencies ACEO and pDEP were the dominant forces for low conductive solutions and nDEP shifted to lower frequency levels with the increasing conductivity of the medium. The regions of pDEP and nDEP on various electrode geometries are demonstrated for the partcles in DI water Manipulation of microparticles by We plan to fabricate a new device for continious cell separation and single cell capturing applications. This study is being supported by TUBITAK under Project No. 111M730.

110 111


A t the present time, the most widely used anode material is graphite; whose theoretical capacity is only 372 mAh g−1 in commercial lithium-ion batteries. However, graphite has some disadvantage such as its capacity obviously insufficient and its energy density rather low. Compared with graphite,

elemental materials that can alloy with lithium, such as Si (4200 mAh g−1), Sn (994 mAh g−1) and Sb (660 mAh g−1), are promising alternative candidates due to their markedly higher capacities. In these candidates, silicon has highest theoretical capacity; nevertheless, silicon anode cannot use as practical application due to its low intrinsic conductivity, poor cycling stability during the insertion and extraction of Li over cell cycling, which consequently leads to the pulverization of the active mass particles, hence permanent capacity fading. There are several ways to overcome this problem, such as decreasing particle-size, using composites with active matrixes such as CNT or graphene due to high electric conductivity and good mechanical properties and inactive matrixes such as Co, Cr, Fe, Mn, Ni, V, Zr, Mo, Ti helps to reduce the mechanical disintegration of the multiphase electrode during cycling.

In this study, core-shell Si/Cu, Si/Ni and Si/Co inactive composite powders were produced by electroless deposition technique and Si/CNT active composite powders were produced by high speed planetary ball milling. The surface morphology of the produced composite powders were characterized using scanning electron microscopy (SEM), equipped with energy dispersive spectroscopy (EDS) for determining the elemental surface composition of the composites. X-ray diffraction (XRD) analysis was performed to investigate the structure of the Si/Ni composite powders. For electrochemical characterization, electrodes were prepared by casting slurry containing composite powders, PVDF and AB on the copper foil. Prepared electrodes cyclically tested between 0.05 V and 1.5 V. In order to investigate electrochemical reaction of the electrode with electrolyte cyclic voltammetry (CV) test was performed. For further electrochemical characterization, electrochemical impedance spectroscopy (EIS) measurements of the produced electrodes were carried out.

*Corresponding Author: [email protected]: Silicon, electrode, active composite, inactive composite, cyclic test, CV, EIS.

Powder Silicon Based Negative Electrodes for

Lithium Ion Batteries

T. Cetinkaya*,

M. Uysal,

M.O. Guler,

H. Akbulut

Sakarya University, Engineering Faculty, Department of Metallurgical & Materials

Engineering

112 113


W ettability of a solid surface can be determined by liquid contact angle measurements [1]. Surfaces that have water contact angle values larger than 150° are called “superhydrophobic” and superhydrophobic surfaces should have tilt angle smaller than 10° and also lower contact

angle hysteresis values [2-4]. Surface roughness and chemical composition are key parameters that affect the superhydrophobic properties of the surfaces. To improve the superhydrophobicity of surfaces, nanoparticles, such as nano tubes, nano-clays and nano-silica are also incorporated into polymers. The introduction of nanoparticles can change the microstructures of polymer matrix which changes the polymer properties [5].

In this work, we firstly investigate the effect of inorganic oxides on surface properties of hydrophobic polyolefines of polypropylene (PP). Later the effect of carbon nanotube (SWCNT) and clay examine on surface properties of PP.

Figure-1: T and R versus l graph of deposited films taken by NKD analyzer (p polarization mode)

The dipping temperature slightly affects the transmittance values of the films until the temperature was reached at 90°C. NKD results indicate that coating at this temperature creates roughness which leads transmittance and reflectance to decrease and contact angle (CA) to increase (Fig.1). Physical and mechanical properties of the polymers are given in Table 1.

The Relationship between

Hydrophobicity and Transmittance

Properties of Polyolefin/Inorganic Oxide

Surfaces

Elbruz Murat Baba 1*

Elif Özen Cansoy 2

and Esra Özkan Zayim 3

1 Nanoscience and Nanoengineering Program, Istanbul Technical University

2 Piri Reis University, Faculty of Science and Letters

1,3 Istanbul Technical University Faculty of Science and Letters, Physics Department

AbstractSurfaces that have water drop contact angle larger than 150° are called “superhydrophobic”. Superhydrophobic surfaces should have tilt angle smaller than 10° and also lower contact angle hysteresis values. In this study, superhydrophobic composite surfaces were synthesized by mixing polyolefin polymers with varying amounts of inorganic oxides such as TiO2, SiO2 and so on. The effect of the amount of inorganic solution concentration on surface wetting properties was also investigated. Optical, structural and mechanical characterizations of the composite surfaces were investigated in detail and the relationship between surface roughness and wettability properties were also examined.

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Table-I Contact angle (CA) values for different temperatures and with different dipping rates.

Decreasing the temperature to 90ºC with dipping rate higher that 1000 mm/min resulted in CA with 137º . Comparing results that have same temperature but different dipping rates indicate that, increasing dipping rate highly affects CA. The highest CA result obtained with the lowest possible temperature and using casting method with SWCNTs which is 164º. Dispersion of clays and SWCNTs were problematic but even without great dispersion CA increase was obtained. In the case of applying tantalum oxide and vanadium oxide inorganic solutions to polymeric surfaces, a decrease was seen in the hydrophobicity of the surfaces. Vanadium oxide is much more hydrophilic when compared with tantanium oxide. When tantalum and vanadium inorganic solutions were used, water contact angle values decreased to 60° and 33°, respectively. Contact angles with different temperature and different dipping rates are given in the Table 2.

Table 2. CA measurement results with different temperature and different dipping rates.

In overall, the dipping rate and the dipping temperature greatly affects CA with creating more roughness. High contact angles were obtained with high dipping rates and the dipping temperature reached at 90ºC.

*Corresponding author: [email protected]. H. Y. Erbil H, Surface Chemistry of Solid and Liquid Interfaces, Blackwell Publishing, (2006). 2. Erbil H. Y., Demirel, L.A., Avci, Y. And Mert O., Science, 2003, 299, 1377.3. Oner, D., McCarthy, T. J., Langmuir, 2000, 16, 7777.4. Erbil, H.Y., Cansoy, C. E., Langmuir, 2009, 25, 14135.5. R. Dufour, M. Harnois, Y. Coffinier, V. Thomy, R. Boukherroub, V. Senez, Langmuir, 2010, 26(22), 17242.

Material Dipping Rate (mm/min) Temperature (ºC) CA

PP 300 130 110º±1

PP 300 90 115º±1

PP >1000 90 137º±1

PP+Clay >1000 100 121º±1

PP+SWCNT >1000 100 133º±2

PP Casting 90 155º±2

PP+Clay Casting 100 163º±1

PP+SWCNT Casting 100 164º±2

Sample Dipping Rate Temperature CA

PP 300 130 110º ±1

PP 300 90 115º±1

PP >1000 90 137º±1

PP + Clay >1000 100 121º ±1

PP + SWCNT >1000 100 133º ±2

PP Casting 90 155º ±2

PP + Clay Casting 100 163º ±1

PP + SWCNT Casting 100 164º ±2

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Dielectrophoresis (DEP) is a non-destructive, electro kinetic transport mechanism with potential for the separation and manipulation of bioparticles in microfluidics devices. With the developments in the MEMS and nanotechnology, a large electric field with weak voltages can

be obtained for manipulating, separating, and characterizing micro/ nano-sized particles such as cells, DNA, proteins, nanotubes, and nanoparticles (Sun and Morgan 2011). In order to make adequate devices the design and simulation should be well correlated to get most feasible and optimum geometry of the electrodes and the microchannel network (Çetin and Li 2011).

Basics of the DEP simulations lies on proper estimation, characterization and us-age of Electrohydrodynamic forces and their effects (Fan, Wang et al. 2007). Simu-lation generally involves the electrical potential field, the flow field and the particle tracing. Simulation of these physical results can be done by a 3D model of the DEP chip on Multiphysics software.

Our work is mainly focuses on cancer cell separation. There are two steps in the work, initial designs and simulations will be performed, after observations and changes correlation of the simulation will be analyzed with experiments.

An initial chip design has been completed and can be seen on figure 1. This general design is a stack of electrode layers on glasses and PDMS as microchannels.

Figure-1: Schematic design of the DEP device

Besides that different alternative electrode configurations can be seen from the figure 2. In the figure 2 (a) and figure 2 (b) only bottom layer includes electrodes,

Simulation and design of a DEP based LOC

device for cancer cell separation

Yavuz Genç,1

Emre Altınağaç, 1

Levent Trabzon, 1,2

and Hüseyin Kızıl 1,3


2 Mechanical Engineering Faculty, Istanbul Technical University

3 Chemical & Metallurgical Engineering Faculty, Istanbul Technical University

AbstractIn the near feature we will see complicated and sophisticated LOC devices for many kinds of medical application which will fit on ones palm and does the job of an high tech laboratory. For enhancing such kinds of devices, the physical and chemical truths, theories, phenomenons will interlace with micro & nano technology. Basicly this abstract will cover the Dielectrophoresis based LOC device design and simulation for cancer cell separation.

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REFERENCESÇetin, B. and D. Li (2011). “Dielectrophoresis in microfluidics technology.” ELECTROPHORESIS 32(18): 2410-2427.Fan, X., H. Wang, et al. (2007). “The use of 2D non-uniform electric field to enhance in situ bioremediation of 2,4-dichlorophenol-contaminated soil.” Journal of Hazardous Materials 148(1–2): 29-37.Sun, T. and H. Morgan (2011). AC Electrokinetic Micro- and Nano-particle Manipulation and CharacterizationElectrokinetics and Electrohydrodynamics in Microsystems. A. Ramos, Springer Vienna. 530: 1-28.

in the Figure 2 (c) and Figure 2 (d) top and bottom includes electrodes in order to give equivalent amount of electrohydrodynamic forces to all fluid flow.

Figure-2: Alternative designs of the electrode configurations

In the figure 3 an initial electric field simulation of the device can be seen where the red areas shows the high electric field regions and blue areas show the lower electric field regions which respectively corresponds to positive and negative DEP locations.

Figure-3: Initial simulations of the electric potential and electric field

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Silica nanoparticles have scientific importance as a research subject due to widely used in various industrial applications, such as catalysis, ceramics, chromatography, electronic and thermal insulators, electronic and thin film substrates, humidity sensors, pharmacy, photographic emulsions and pigments [1, 2]. Monodisperse

silica colloidal particles have been used in the preparation of three-dimensional photonic crystals recently, and the average size and size distribution of these particles strongly affects the quality of these products [2].

Monodisperse spherical silica particles in the colloidal size range can be synthesized via the well known Stöber method. Stöber et al. showed that ammonia catalyzed reaction of tetraalkyl silicates with water in alcoholic solutions leads to produce spherical silica particles with uniform shape and very narrow size distribution in the size range from 50 nanometers to 2000 nanometers in diameter [3]. The synthesis procedure is based on the following two-step chemical reactions. First, hydrolysis of alkyl silicates, Equation (1), and then subsequent condensation of silicic acid, Equation (2), in alcoholic solutions [4].

Si(OC2 H5 )4 + 4H2 O ➝ Si(OH)4 + 4C2 H5 OH (1)Si(OH)4 ➝ SiO2 + 2H2 O (2)

Bogush et al. extended Stöber’s work by studying a wide set of reagent concentrations and reaction temperatures which result monodisperse silica precipitates with narrow size distributions [5]. They derived a correlation using their experimental results to predict the final particle size from the initial reagent concentrations. The presented correlation is a very useful tool when tailoring particle size for particular needs. A seeded growth technique was introduced by Bogush et al. in order to obtain both larger particles and higher solid mass fractions.

Van Blaaderen et al. investigated the formation and growth mechanisms of silica particles prepared by the Stöber method [4]. Beganskiene et al. investigated the sol-gel process in non-aqueous system of tetraethyl orthosilicate (TEOS) using various characterization techniques and optimized the reaction parameters to produce monodisperse spherical silica nanoparticles suitable for to use in the development of antireflection coating technology [6]. Zhang et al. studied the effects of dilution of TEOS with ethanol on the shape and monodispersity of silica particles [2].

In the context of this paper, highly monodisperse spherical silica colloidal particles of sub-500 nm in diameters were synthesized using the Stöber process. An extensive experimental study was performed to determine the effects of initial reagent concentrations

Spherical Silica Colloidal Particles: An Experimental Study on the Particle Shape and

Size Distribution

Mumin Balaban1, 2*

Levent Trabzon1, 2, 3

and Huseyin Kizil1, 2, 4


Istanbul Technical University2 ITU MEMS - Nano/Microelectromechanical

Systems R&D Center, Istanbul Technical University


4 Faculty of Chemical & Metallurgical Engineering, Istanbul Technical University

AbstractIn this paper, we present a comprehensive experimental investigation for the effects of initial reagent concentrations and reaction temperature on the average size and size distribution of spherical silica colloidal particles. Stöber method was used for the synthesis experiments, and the water-tetraethyl orthosilicate (TEOS)-ammonium hydroxide-ethanol system was studied for a complete set of initial reagent concentrations (H2O: 0.5-17.0 M, TEOS: 0.15-0.25 M, NH4OH: 0.25-2.75 M) and at different reaction temperatures (25-35 °C). Highly successful results were obtained for the particle shape and size distribution.

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and reaction temperature on the average size and size distribution of the Stöber silica particles. A total number of 38 experiments were done for a complete set of initial reagent concentrations (H2O: 0.5-17.0 M, TEOS: 0.15-0.25 M, NH4OH: 0.25-2.75 M) and at different reaction temperatures (25-35 °C). Highly successful results for particle shape, as well as size distribution, were obtained (See Figure 1).

Figure-1: Selected SEM image. Average particle size of 223.0 nm with a standard deviation of 12.6% was obtained for the experimental conditions of

0.15 M TEOS, 0.75 M NH4OH, 15.00 M H2O and at room temperature.

For low water concentration of 0.5 M, as well as low ammonium hydroxide concentration of 0.25 M, non-spherical particles were grown. Although there are some exceptions, looking at the experiment results it is seen that there is a general tendency towards lower standard deviations for higher average particle sizes. The presented results in this work give very valuable information when designing the experimental conditions to achieve the targeted average particle size and standard deviation. However, we note that a further extensive study on the reproducibility of the experiment results is required.

*Corresponding author: [email protected][1] H. Giesche, Journal of the European Ceramic Society 14, 3 (1994).[2] J. H. Zhang et al., Journal of materials research 18, 3 (2003).[3] W. Stöber et al., Journal of colloid and interface science 26, 1 (1968).[4] A. Van Blaaderen et al., Journal of colloid and interface science 154, 2 (1992).[5] G. H. Bogush et al., Journal of Non-Crystalline Solids 104, 1 (1988).[6] A. Beganskiene et al., Mater Sci (Medžiagotyra) 10, (2004).

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P hotochromism (PC, for short) has been described as a reversible change in the color, or darkening of a material caused by absorption of more generally ultraviolet or visible light [1, 2]. The color change is often attributed to alteration in the structure of the compound [3, 4]. In principle, both inorganic and organic

materials can represent photochromic properties. Tungsten oxide has been regarded as the best candidate for chromogenic applications amongst inorganic materials because of its relatively high stability, durability, multifunctional properties as well as its high color efficiency.

In this work, we describe a procedure for tungsten oxide from tungsten hexachloride as precursor, exhibiting reversible photochromic properties, improved stability and life-time. Also, this procedure permits us to fabricate films as either nanofibers or microfibers, displaying photochromic effects. Furthermore, we have prepared thin films and microfibers of the organic/inorganic blend of tungsten hexachloride (WCl6) and PVP, via electrospinning, spin coating, droplet drawing, casting and writing ink, given that the technique to prepare tungsten oxide is the prime determinant of size of the fibers and formation of the film. Our results indicate that tungsten oxide in the form of films and microfibers has PC properties offer numerous advantages such as (i) the color change is relatively rapid, (ii) they have large optical modulation and last (iii) they possess long memory and long life-time. In overall, we believe that this reported procedure is an avenue to prepare photochromic materials, with superior properties.

SEM images of electrospun nanofibers of the solution are presented in Figure-1. The diameters of the nanofibers are distributed in the range of 190–350 nm with an average diameter of 270 nm, as shown in the inset. The electrospun microfibers displayed in Figure-2 represent color alteration under UV lamp acting as a UV detector and return to their original state after a while when the UV lamp is switched off. It is worth noting that reversible fully coloration process takes about 3 minutes while the bleaching process takes about 3 hours, which indicates that the photochromic fiber has a good memory effect. More importantly, the color-cycle of the material is reversible and it retains its durability and reversibility over long period of time (i.g., several months).

Synthesis and Analysis of

Tungsten Oxide-Based

Chromogenic Systems

Amin Tabatabaei Mohseni 1

Esra Özkan Zayim 1,2


2 Physics Engineering Department, Faculty of Science and Letters,

Istanbul Technical University

AbstractWe describe a procedure to prepare thin films and microfibers of the organic/inorganic blend of tungsten hexachloride and polyvinylpyrrolidone. Herein, we report that the procedure offers several advantages over previously known procedures in the literature. It allows fabrication of films and microfibers, exhibiting reversible color change. Tungsten oxide fabricated via this procedure as nanofibers, microfibers and thin films, can be applied to numerous types of surfaces with different techniques. These materials have large optical modulation and possess long memory with superior life-time. In overall, we believe that this procedure is an avenue to prepare reversible photochromic materials, with superior properties.

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Figure-3: Spin-coated films of tungsten oxide. (a) as-prepared; (b) after 8 minutes of UV exposure.

In overall, tungsten oxide coating present new opportunities for non-destructive writable optical memory. Their long-term stability and environmental durability leads to develop new organic/inorganic photochromic materials that be processed from microfibers to large-area solid films displaying excellent photochromic properties. Another advantage of this blend is to be applicable to various types of substrates, such as glass, ITO glass, metal and paper.

[1] H. Dürr, H. Bouas-Laurent. Photochromism: Molecules and Systems. (ELSEVIER, 2003).[2] P. Bamfield, Chromic Phenomena, The Technological Applications of Colour Chemistry. (RCS, 2002).[3] Y. He, Z. Wu, L. Fu, C. Li, Y. Miao, L. Cao, H. Fan and B. Zou, Aqueous Sol. Chem. Mater. 15, 4039-4045 (2003).[4 K. Kim, C. Seo and H. Cheong, Korean Physical Society. 48, 1657-1660 (June 2006).

We also spin-coated the blend on glass substrate at room temperature with speed of 2000 rpm. Figure-3 shows the effect of UV exposure on the spin-coated thin films after 3 minutes. Away from direct UV light source in the darkness or in visible light, the bleaching process takes about 3 hours.

Figure-1: SEM images of electrospun nanofibers of tungsten oxide.(a) 5µm scale; (b) 1µm scale.

Figure-2: Electrospun microfibers of tungsten oxide. (a) as-prepared macroscopic image; (b) UV irradiated macroscopic image; (c) as-prepared

microscopic image; (d) UV irradiated microscopic image.

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