MAKING A MICROWAVE DRIVEN ACTUATOR BY INTERPENETRATION OF A CONDUCTIVE POLYMER IN A THERMOSENSITIVE HYDROGEL.

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

Congreso; 10th International Conference on Frontiers of Polymers and Advanced Materials; 2009

Crosslinked acrylamide based hydrogels are interesting candidates for technological applications, such as drug release.[1] Specifically, hydrogels sensitive to external parameters (pH, temperature, ionic force, electric field, etc) constitute the so called “smart” hydrogels which could react actively to changes in the environment.[2] The materials could also 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 action. Most of the external actions involve slow changes in the complete environment of the gel. It would be most interesting to induce the volume change at a distance using electromagnetic radiation. Indeed, smart hydrogels driven by NIR radiation absorption has been proposed.[3] It is known that conductive polymers absorb strongly electromagnetic radiation, specifically in the microwave range, with heating up of the polymer. [4] By compositing a smart (thermosensitive) hydrogel matrix with a conductive polymer it would be possible to induce the hydrogel temperature transition using microwave radiation. In the present communication the use of polyaniline (PANI), semi-interpenetrated (sIPN) inside thermosensitive poly(N-isopropylacrylamide) (PNIPAM) based network hydrogels, to induce a phase transition by microwave absorption is demonstrated.. The incorporation of a conductive polymer makes the hydrogel sensitive to microwave radiation. Upon irradiation, 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 drug (propanolol) driven by microwave irradiation is demonstrated. A similar effect is observed when polypyrrole (PPy) is interpenetrated into PNIPAM. In this case, pH has no effect on the microwave absorption nor in the transition. On the other hand, both PANI and PPy interpenetrated thermosenistive hydogels, show strongly decreased sensitivity when the conductive polymer is reduced.