Polyurethane composites containing spherical and flake-shaped silver fillers of micrometer and nanometer sizes were prepared by reacting suspensions of the silver filler in tetraethylene glycol with Desmodur® HL BA. Both the thermal conductivity and the stability of the silver composites are increased in comparison with a reference polyurethane sample without filler. Unexpectedly, the largest increases in thermal conductivity and stability are observed for the spherical silver particles of micrometer size but not for the silver nanoparticles, which is reasoned with larger aggregates of silver particles and a higher degree of crystallinity in the sample containing micrometer-sized silver particles.

Thermal conductivity of polyurethane composites containing nanometer- and micrometer-sized silver particles

Silver particulate thin films on softened polymer blends of Polystyrene (PS)/Poly(2-vinyl pyridine) (P2VP), PS/Poly(4-vinylpyridine) (P4VP), and Poly(vinylpyrollidone) (PVP)/P4VP at a rate of 0.4 nm/s held at a temperature of 457 K in vacuum of 8 × 10-6 Torr by evaporation are deposited. These silver films were characterized by their electrical behavior, optical properties and Scanning electron microscopy (SEM). Silver films deposited on softened PS, and PVP give rise to a very high room temperature resistance approaching that of the substrate resistance due to the formation of a highly agglomerated structure. On the other hand, silver films on softened P2VP and P4VP give rise to a room temperature resistance in the range of tens to a few hundred MΩ/ which is desirable for device applications. Silver films on the composites of PS/P2VP, PS/P4VP and PVP/P4VP show resistances at room temperature. The optical and plasmonic response of Ag nanoparticles onto thin layers of blends shows encapsulation of nanoparticles. The electrical properties and SEM of silver nanoparticles on the thin layers of polymer blends indicate the formation of much smaller, narrower dispersion and wide size distribution.

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Preparation and Characterization of Subsurface Silver Particulate Films on Polymer Blends of Polystyrene/Poly(2-vinylpyridine)/Poly(vinylpyrollidone)/Poly(4-vinylpyridine)

It is difficult to disperse silver nanoparticle homogeneously into a polymer matrix by ex situ methods because of easy agglomeration of nanoparticles. At present, it is possible to obtain nanoparticles of different shape and size in nanostructured polymeric environment using various polymeric systems and different approaches. Numerous methods used toxic and potentially hazardous reactants. Increasing environmental concerns over synthesis route resulted in an attempt to adopt eco friendly methods.

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Silver Particulate Films on Compatible Softened Polymer Composites

Yellow transparent polyurethane-co-polystyrene films containing silver nanoparticles could be synthesized. Silver nanoparticles and transparent polymer film making up nanocomposite films were formed simultaneously through radical initiated polymerization of amphiphilic urethane acrylate, nonionomer (UAN)/styrene/silver nitrate mixtures. Size of silver nanoparticle could be controlled by varying weight ratio of styrene in UAN/styrene mixtures and chain length of PEO and PPO segment in UAN chain, which are much easier process compared to the synthetic process of nanoparticles using amphiphilic block copolymers. Formation of silver nanoparticles and change of nanoparticle size could be conformed by transmission electron microscopy and characteristic UV absorbance spectra. Tensile modulus and glass transition temperature of polyurethane-co-polystyrene films were drastically increased at 0.45 wt% of silver nanoparticles embedded at their matrix, indicating that silver nanoparticles embedded at polymer films can act as an inorganic nanofiller for improving mechanical property.

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Papers

Amphiphilic Polyurethane-co-polystyrene Network Films Containing Silver Nanoparticles