Diffusion of Molecular Probes in Thermoresponsive Poly(N-isopropylacrylamide) Hydrogels: Electroanalytical Studies

Abstract

Abstract : Poly(N-isopropylacrylamide), NIPA, thermoresponsive hydrogels with well defined concentrations of an electroactive probe, 1,1'-ferrocenedimethanol, Fc(MeOH)2, were prepared. The discontinuous reversible volume phase transition of such gels occurs at 32 +/- deg C, and results in a release of approximately 93% of the solvent from the polymeric network. Transport of Fc(MeOH)2 in both swollen and collapsed gels was studied using steady state voltammetry and chronoamperometry at platinum microelectrodes. The diffusion coefficient of Fc(MeOH)2 in collapsed gels was approximately two orders of magnitude smaller than that in swollen gels. UV/vis spectroscopic studies shown that for a 3.0% NIPA gel the concentration of Fc(MeOH)2 in collapsed gel phase was approximately 6 time higher than that in released solution and 4.5 times higher than in the original swollen gel.