Conductive photopolymers : Insitu synthesis of metal nanoparticles

A prologue to the field of noble metal nanoparticles is presented with a brief commentary on the basic synthesis techniques to manufacture these metal nanoparticles and to exploit the full use of their unique properties. In recent years scientific interest in embedding the metal nanoparticles in a host polymer has been increased significantly. A great advancement in the field of conductive polymers by embedding metal nanoparticles in them has been witnessed because they are likely to be an alternative to the conventional conductors. There are different available techniques in use these days to prepare these polymer-metal nanocomposites. However, photopolymerization is gaining a lot more attention mainly because of some extra ordinary advantages. This is one of the most effective ways to convert liquid monomers into polymer materials upon irradiation of UV light. Furthermore, embedding of nanoscopic metal particles in polymer matrices is with the help of free radical photopolymerization technique is one of the easiest and fastest ways. Photocured polymeric films are a promising candidate for the realization of flexible electronics, due to their easy processability, low cost, and availability. The objective of this thesis is to synthesize and stabilize two different kinds of noble metal nanoparticles i.e. silver and copper nanoparticles in an acrylic resin. In order to carry out this research, the quality of obtained nanoparticles was examined with respect to the nature of substrates, irradiation time, and monomer/salt ratio. In the first half of this research, electrically conductive UV-cured films have been prepared by irradiating an acrylic difunctional monomer in the presence of silver nitrate, pyrrole, and a photoinitiator. Homogeneously dispersed silver nanoparticles (size range 50–80nm) embedded by polypyrrole formed throughout the acrylic matrix. Interestingly, the electrical conductivity of the acrylic films increased a hundred times after the formation of the Ag polypyrrole nanoparticles. Evaluation of the irradiation process was conducted by UV–Vis spectroscopy using model systems where the acrylic monomer was substituted by a solvent. It has been shown that as a function of composition and irradiation time there is a simultaneous reduction of silver nitrate and pyrrole polymerization forming silver nanoparticles covered by the conductive polymer. The effect of PVP concentration on the different properties of silver nanoparticles was investigated. It was ascertained that there is a significant influence on the morphology of silver nanoparticles. The second half of this research is to synthesize copper nanoparticles. Synthesis of the less stable copper nanoparticles is more difficult and challenging because copper nanopaticles are easily oxidized. Different stabilizing agents like poly(N-vinylpyrrolidone) (PVP), pyrrole, sodium L-ascorbate are used as capping agents to prevent the aggregation and to stabilize the obtained copper nanoparticles against oxidation. The copper nanoparticles obtained were characterized by UV-vis absorption spectra, dynamic light scattering, scanning transmission electron microscopy and FESEM. It has been observed that the particle size and particle size distribution influenced significantly in the presence of PVP. However, there is no substantial effect observed by adding pyrrole as a stabilizer.