A microwave driven smart hydrogel: Poly(n-isopropylacrylamide) based network semi-interpenetrated with polyaniline

MOLINA M.A.; RIVAROLA C.R; BARBERO C.A.

Bariloche

Workshop; US-Argentine Workshop on Nanomaterials; 2009

Crosslinked acrylamide based hydrogels are interesting candidates for technological applications, such as drug release. Specifically, smart hydrogels react actively to changes in external parameters (pH, temperature, etc). The materials could be used in chemical or mechanical actuators since they change volume and expel a significant amount of its inner solution when a transition is induced by external stimuli. Most of those stimuli involve slow changes in the complete environment of the gel, which is cumbersome for fast actuation. On the other hand, it is known that conductive polymers absorb strongly electromagnetic radiation, specifically in the microwave range, with heating up of the polymer. By compositing a smart (thermosensitive) hydrogel matrix with a conductive polymer it should be possible to induce the hydrogel temperature transition using microwave radiation. Crosslinked poly(Nisopropylacrylamide) hydrogels were semi-interpenetrated with polyaniline chains by oxidative polymerization of aniline on a preformed gel. Upon irradiation with microwaves, the conductive matrix heats up driving the phase transition of the gel which involves a clear volume decrease. The effect is modulated by pH which control the conductive/insulator transition of polyaniline. Successful liberation of a probe molecule driven by microwave irradiation is demonstrated. The molecular nature of the compositing process and response mechanism makes it amenable to the formation of smart nanomaterials.