Light-Sensitive Gas Sensors Based on Thiol-Functionalized N-Isopropylacrylamide Polymer-Gold Nanoparticle Composite Films

Random and block N-isopropylacrylamide (NIPAM)/cysteamine copolymers and a thiol-terminated NIPAM homopolymer have been synthesized, characterized, and covalently linked to gold nanoparticles. Electrical conductivities of their films have been measured as a function of temperature and laser irradiation wavelength in the presence of water, methanol, and hexanes vapors. For the homopolymer composite, the distance between particles is so large that the conductivity is negligible. For the block copolymer composite, changes in dielectric constant dominate film conductivity due to coating of the gold particles. The random copolymer composite film changes conductivity dramatically in the presence of water and methanol vapors upon heating because of swelling/shrinking of the NIPAM. Laser irradiation with light matching the energy of the surface plasmon resonance of the gold nanoparticles causes dramatic changes in the conductivity of the composite film in the presence of water vapor. However, minimal changes occur for the corresponding film of the block copolymer.