| Three different thiol-functionalized homo, random, and block NIPAM polymers, specifically PNIPAM-thiol, poly(NIPAM-stat-cysteamine) and poly(NIPAM-b-cysteamine), have been synthesized and characterized by 1H-NMR and size exclusion chromatography (SEC). These have been covalently linked to gold nanoparticles, and the composites have been characterized by UV-Vis spectroscopy, dynamic light scattering (DLS), electron microscopy and X-ray photoelectron spectroscopy. Electrical conductivities of drop-cast films of these composites have been measured as a function of temperature and laser irradiation in the presence of different gases and vapors. It is found that for the PNIPAMthiol polymer, the distance between the gold particles is so large that the conductivity of the film is negligible. For the case of the block copolymer, changes in the dielectric constant of the films dominate the measurements due to the fact that the gold particles are coated by the cysteamine blocks and relatively far apart (but not as much as for the PNIPAM-thiol polymer). The random copolymer exhibits changes in conductivity due to heating (either directly or by laser irradiation) that may be explained by changes in the distance of the gold nanoparticles that occur due to temperature-induced morphology changes of the NIPAM. |
