Voltammetric studies of transport properties of poly(N-isopropylacrylamide-co-acrylic acid) gels swollen by methanol

The electro-oxidation of methanol at a platinum microelectrode in poly(N-isopropylacrylamide-co-acrylic acid) (NIPA-AA) gels was studied as a function of temperature. Diffusion coefficients of methanol in NIPA AA gels of various copolymer concentrations were determined from the steady-state voltammetric currents over the temperature range 5-55 degrees C. Transport parameters (diffusion coefficients and activation energies of diffusion) were compared to those for undiluted methanol, and related to the transport properties of uncharged probe molecules of 1, 1'-ferrocenedimethanol in both liquid and gel media. Diffusion of uncharged species, methanol and 1, 1'-ferrocenedimethanol, in the gels was as fast as in liquid media, with diffusion coefficients close to 1 X 10(-9) m(2)/s for both species at 25 degrees C. Activation energies of diffusion for methanol and 1, 1'-ferrocenedimethanol in the gels were smaller than those observed in liquid media, they did not depend on the copolymer concentration in the range 1.3-2.5%; and their average values were 9.3 +/- 0.4 and 11.8 +/- 0.7 kJ/mol for methanol and 1, 1'-ferrocenedimethanol, respectively. (C) 2000 The Electrochemical Society. S0013-4651(99)08-073-8. All rights reserved.