Voltammetric Studies of Transport Properties of Poly(N-isopropylacrylamide-co-acrylic acid) Gels Swollen by Methanol

Wojciech Hyk and Malgorzata Ciszkowska*

Department of Chemistry, Brooklyn College, The City University of New York, Brooklyn, New York 11210-2889

Abstract:

The electrooxidation 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 ^oC.  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 1x10^-9 m²/s for both species at 25 ^oC.
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.