Polymer Nano Composites

References:1.Ash B.J. Polymer Nanocomposites with Particle and Carbon Nanotube Fillers, Dekker Encyclopedia of Nanoscience and Nanotechnology.2.Springer Handbook of Nanotechnology Editor Bhushan3.Synthesis of Inorganic Materials by Ulrich Schubert4. Caruso, F. Nanoengineering of particle surfaces.Adv. Mater. 2001, 13, 11–22.

Dr. AMIR HABIB

Introduction

• Polymer nano composites (PNCs) are composites with polymer matrix and a filler with at least one dimensions less than 100nm

• Fillers may be plate like clays, high aspect ratio NTs and lower aspect ratio or equiaxed nanoparticles.

Examples from Nature and Old Use

• Carbon black and fumed silica filled polymers have been used over a century.

• Diatoms, like radiolaria represent the incredible control Nature exerts over the assembly of organic-inorganic materials.

Recent increased interest • Our ability to synthesis and manipulate alot of

nanofillers. • Nanoparticle and NT filled composites´

uniqueness over traditional composites.• Large changes in material properties require

small nanofiller loadings.

• Uniqueness of Nanofiller to micronfilled composites.

• Surface modification of nanofillers.

• Examples of mechanical, electrical and optical properties in nanoparticle/nanotube filled polymers.

Outline

What makes Nanocomposites Unique

• Small Size• Small mechanical, optical and electrical

defects.• No decrease in ductility of the polymer.• Do not scatter light below 50nm.• Nanofillers do not concentrate electro-

magnetic fields.

• Decrease in melting point of Au nano particle

• CdSe colloidal suspension

• Magnetization and Charge storing capacity;e.g., BaTiO3 nano particles.

Nanomaterial;Different from their bulk

Interfacial Area and Interparticle Spacing

• Small size leads to large interfacial area.

• Interparticle spacing (~100A°) decrease at even small volume fractions of filler.

Interaction Zone

• Interaction zone(IZ (~ 2-9nm thick) is the region where structure and properties of the filler are changed.

• IZ; a region of altered chemistry, polymer conformation, chain mobility, degree of cure, or crystallinity.

Challanges in processing nanofillers

• Dispersion of nano particles and nanotubes.

• Controlling the size and the agglomeration of nanofillers.

• Large radius of curvature and increase in surface energy.

Methods of Surface Modification of Nanoparticles

• Silanes and organotitanates are used to link the surrounding matrix and to lower the surface energy of nanoparticels.

• Radiation grafting.

• Chemical Vapour Depositon.

• Polymerize polymer chains off of initiating agents coupled to the surface.

Surface Modification of CNTs

• MWNT are easily separated by sonication.

• SWNT exfoliation is more difficult i.e.,without shortening and introducing defects.

• Dispersing them uniformly in poymer matrix and preventing agglomeration is achieved by attaching functional groups.

SWNTs

Chemical Methods of Modification

• Noncovalent surface modification of nanoparticles and CNTs

• Covalent attachment of chemical groups to nano particles and walls of nanotubes

Noncovalent surface modification of CNTs

• Noncovalent surface modification of CNT include all treatments that cause a change in the functional groups that face the solvent (or the polymer), without modifying chemical nature of NT.

• Advantage of noncovalent modification is; the basic structure and hence the mechanical and eletrical properties are not changed.

• Noncovalent attachement is possible if there is a secondary bonding between these groups and the surface of NT.

• Attack of defect sites

by nitric acid, forming carboxylic acid gropus.

• The resultant carboxy-lated NTs can further covalently modified by reactions based on the carboxylic acid groups.

Covalent attachment of chemical groups to walls of Nanotubes

Other types of Covalent surface modifications.

Mechanical Properties• Improvement in yield stress 30% and Young

modulus 170% in nano filled polypropylene compared to micron filled polypropylene

• Nylon 6 filled with 50nm silica NPs showed increase in tensile strength 15%, strain to failure 150%, Youngs modulus 23%, and impact strength 78% with only 5 wt.% NPs.

• The load transfer to MWNTs dispersed in an epoxy resin was much higher in compression than in tension.

Thermal properties

• Important from mechanical stability and processing perspective.

• Tg changes as function of filler content; increase/decrease in Tg reported is linked to immobilization of the matrix within IZ.

• Industrial epoxy loaded with 1wt% SWNTs showed an increase in thermal conductivity of 70% and 125% at 40K and at room temperature, respectively.

Optical properties

• Clarity for visible wavelengths,adding nano particles/tubes can as well introduce additional functionality in form of UV absorption & alteration of refractive index of polymer.

• TiO2 NPs to polymers

• NCs of leadsulfide & polyethylene oxide increases refractive index to 3.9

• Gold NPs in gelatin reduce ref. Ind. to 1

• In these NCs interaction with polarized light vary with direction and intensity of light.

Electrical properties

• NCs have enhanced properties like conductive polymers, superpara magnetism in magnetic material.

• Percolation threshold has been shown to lower in NCs than traditional Cs.

• The dielectric breakdown strength of NCs can be enhanced over compositions with micron-scale fillers.

• Organic-inorganic NCs as etch resists showed improved rigidity and higher Tg which enhaces resist performance for nm pattern fabrication.

Conclusion

• PNCs are a novel class of composites.

• Choice is between SWNTs and MWNTs in case of NTs.

• Tailoring the nanoparticle/tube-matrix interface is a challenge and a topic of current interest for scientists.

Thanks