Photoinduced Silver Precursor Decomposition for Particle Modification in Tungsten Oxide-Polymer Matrix Nanocomposites

A processing technique based on optical excitation of a polymer matrix nanocomposite containing a chemical precursor is presented to demonstrate the potential of this process for localized modification of nanoparticles in the bulk of the material. Femtosecond laser irradiation of a nanocomposite consisting of tungsten oxide nanoparticles in a fluoropolymer (tetrafluoroethylene-co-hexafluoropropylene) matrix resulted in decomposition of a silver precursor (vinyltriethylsilane-(hexafluoroacetylacetonate)silver(I)). Transmission electron microscopy (TEM) results showed an increase in particle size as a result of photoprocessing with particles displaying core-shell type architectures. Optical absorption spectroscopy measurements indicated that silver was deposited in the bulk of the material and were consistent with absorption cross-section models for tungsten oxide core/silver shell nanoparticles. Estimates for silver shell volumes were found to correlate with the surface areas of the base tungsten oxide particles. Modeled results for photothermal temperature rises suggest that thermal processes are probably not responsible for precursor decomposition and the most likely mechanism is multiphoton, photocatalytic precursor decomposition at the surface of the tungsten oxide nanoparticles because tungsten oxide is a known photocatalyst. Models for precursor diffusion in the matrix after particle excitation are used to identify relevant time scales associated with precursor depletion and to provide additional insight into this in situ deposition process for particle modification.