Construction of multifunctional materials by intrachannel modification of NIPA hydrogel with PANI-metal composites

Composites containing conductive polymers and Au and Ag nanoparticles were introduced into the environmentally sensitive poly(N-isopropylacrylamide) hydrogel channels. The composites were synthesized directly in the channels by two phase polymerization procedure. In the first step the unmodified hydrogel was placed in a solution containing the oxidizing agent (HAuCl4 or AgNO3), and in the second step it was placed in a solution of aniline in nitrobenzene. The presence of polyaniline and metal nanoparticles increased conductivity of both types (ionic and electron) while the hydrogel properties, such as: flexibility, plasticity and ability to phase transition, were preserved. The presence of nobel-metal nanostructures added catalytical activity to the new materials. Optical and SEM investigations revealed that polymer-metal composites were uniformly distributed in the entire gel samples. NIPA-PANI-Au composites exhibited a sharp volume phase transition in response to changes in temperature and ionic strength. That behavior was similar to unmodified poly (N-isopropylacrylamide) hydrogel. The new material was electroactive and had electrocatalytical properties towards electrooxidation of ethanol. Electroactivity of the modified gel was a strong function of the swelling ratio; the shrinking process enhanced the voltammetric response.