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
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.