ravi self cleaning

8/23/2019 Ravi Self Cleaning

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Self cleaning smart coating

Ravindra Marathe

M.Sc M.Tech

Under the Guidance of

Dr. V.V.Gite

M.Sc. Ph.D

School of Chemical Science,

North Maharashtra University, Jalgaon,

Maharashtra- 425001


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Introduction Many technologies existing in todays world have been derived

from nature. Self-cleaning is one amongst them.

Many surfaces in nature exhibit self-cleaning properties. E.g.

The wings of butterflies and the leaves of plants, such as

cabbage and lotus.

this technology received a great deal of attention during the

late 20th century

E.g. window glass cleaning, solar panel cleaning and cements to Thetextiles


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Aim & objective of self cleaning coatings

Develop highly efficient and durable self-cleaning coating

surfaces with enhanced optical qualities.

which include reduction in maintenance cost.

elimination of tedious manual effort

reduction in the time spent in cleaning work.


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Why self cleaning surface to clean surface of buildingmaterials causes ?

Considerable trouble.

High consumption of energy.

Chemical detergents High costs


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Classification of self cleaning coatingsClassified into two major group

hydrophilic

hydrophobic.

Both of the categories clean themselves by the action of water.

In a hydrophilic coating- the water is made to spread (sheeting of

water) over the surfaces, which carries away the dirt and other

impurities.

In hydrophobic technique- the water droplets slide and roll over

the surfaces thereby cleaning them.

E.g. metal Oxide


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What is self cleaning effect?

The self-cleaning phenomenon is related to the surface contactangle. It is the angle formed at the three phase boundary (solid/

liquid/vapour) between the surfaces of the liquid drop to the

surface of the solid. In general, if the contact angle is 90, the surface is defined as a hydrophobic surface.

Similarly, a surface with a water contact angle approaching zero is

classified as ultra (super) hydrophilic and a surface with a contactangle >150 is usually categorized as ultra (super) hydrophobic

Fig. 1 A schematic representation of hydrophilic, hydrophobic and ultra (super) hydrophobic surfaces.


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Hydrophobic coatings Nature is the source of inspiration for many around the world to

develop aesthetic self-cleaning functional systems.

e.g. lotus flower

The mystery behind this mechanism was unfolded after the invention

of the SEM in mid 1960s.

Studies made using SEM revealed that the lotus surfaces --macroscopically smooth,

-Exhibit microscopic roughness on different scale lengths.-Epicuticular wax crystalloids, make the leaves super-hydrophobic.


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there are two major types of surface in plant leaves withsuperhydrophobicity:

(i) hierarchical micro and nanostructures.

(ii) unitary micro-line structures.


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Plant leaves with hierarchical structure

Fig. a and b are SEM images of lotus leaf

surface

-Flanges 310 mm sized.

-valleys tinted with a 70

100 nm sized

wax like material.

-(Fig. a). A lot of nanorod like structures

with an average diameter of about 50 nm

-The water contact angle observed is

around 162.


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Fig. c and d show the SEM images ofrice leaf.

-The top surface of the leaf posses thepapillae

-Average diameter of about 58 mm

-they are arranged in one-dimensional order

Fig. d) The sub layer of the surface

consists of

- Nanopins that are proportionally well

distributed to the air trapping mechanism

in the surface

-(Fig.d). The water contact angle of

surface is 157


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Plant leaves with unitary structure.

This unique structure is also found on the surfaces of Chinese

watermelon shown in Fig. c and d. Surprisingly, the surface

morphologies of ramee leaf and Chinese watermelon are fibers and

both exhibit a WCA of 159

Fig. shows the SEM images of unitary structures exhibited by different plant leaves.


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Materials and mechanism to produce self cleaning coatings

Inspired by the self cleaning coating exhibited by nature, researchers

around the world started working on developing technologies to produce

surfaces with extremely low surface energies and also to control the

morphology of the surface on a micron and nano-metre scale. This ideaof controlling surface morphology opens up many possibilities for

developing a variety of engineered surfaces.

Techniques to produce hydrophobic and super-hydrophobic surfaces

classified into following categories:

a) making a rough surface from a low surface energy material;


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Roughening the surface of low surface energymaterialSilicones

Fluorocarbons

Organic materials

In-Organic materials


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Making a rough surface and modifying the surface withmaterial of low surface energy

In the past few years to fabricate rough surfaces and subsequently

modifying the surface chemistry to produce super-hydrophobic

membranes.

1. Wet chemical reaction and hydrothermal reaction.2. Electrochemical deposition.

3.Lithography.

4.Self-assembly and layer-by-layer (LBL) methods.

5.Electro-spinning technique.

6.Etching and chemical vapour deposition.

7.Solgel method and polymerization reaction


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Hydrophilic photo-catalytic coatings

Unlike hydrophobic/super-hydrophobic surfaces that rely solely on the

flow of water to clean the surface, hydrophilic coatings chemically

break down dirt and other impurities when exposed to sunlight.

This process is called photo-catalysis. The technique is basically

inspired from the process of the green leaves, which uses sunlight to

drive the chemistry.

Although a few products that work on the principle of hydrophilicity

are, this field is far from attaining maturity. Research works are under

way in developing hydrophilic self-cleaning coatings and there are

regular publications in this field.


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Functions of hydrophobic surfaces

Fig. Functions of super-hydrophobic surfaces.


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Characterization techniques

UV

TEM

FTIR

X-ray analyzes

(FE-SEM)

contact angle Goniometer

Atomic force microscopy (AFM)


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Applications of self-cleaning coatings

Textile industry (self-cleaning clothing).

Automobile industry (self-cleaning windshield glass, car bodies

and mirrors).

Optical industry (cameras, sensors, lenses and).

Marine industry (anticorrosion protection).

Aerospace industry (non sticky surfaces).

Self-cleaning coatings can also be used in windows (windowcoatings).

Solar modules (self-cleaning coatings for solar modules).

paints (exterior paints with self-cleaning).


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Conclusion The self cleaning surface on naturally occurring leaves and wings

of certain insects is multipurpose in achieving self-cleaning, anti-

reflective, and various other functionalities which has got

researchers across the globe take stock and attempt to mimic.

Though the self cleaning surfaces by them are yet to match

their naturally occurring, the fabrication techniques have indeed

evolved into more environmentally compatible and cost-effective.


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Reference

1 http://www.activglass.com/index_eng.htm. http://www.ppg.com/. A. Marmur, Langmuir, 2004, 20, 3517. A review on self-cleaning coatings. Hemant Kumar Raut, A. Sreekumaran

Nair and Seeram Ramakrishna V. Anand Ganesh, Cite this: J. Mater.

Chem., 2011, 21, 16304 Z. Cerman, A. Solga, B. F. Striffler, M. Spaeth and W. Barthlott,

Bioinspir. Biomimetics, 2007, 2, S126134. U. Mock, W. Menz and J. Ruhe, J. Phys.: Condens. Matter, 2005, 17, 595605.

Otten and S. Herminghaus, Langmuir, 2004, 20, 24052408. M. H. Sun, C. X. Luo, L. P. Xu, H. Ji, Q. Ouyang, D. P. Yu and Y. Chen, Langmuir, 2005, 21, 8978.


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