Electrochemical and structural characterizations of an experimental track-etched membrane in KCl solutions

Characteristic electrochemical transport parameters for an experimental pol y(ethylene)terephtalate (PET) track-etched membrane with well-defined struc ture and low porosity (Theta = 0.13%) were determined with the membrane in contact with KCl solutions at different concentrations. Membrane potential, Delta phi(m), measurements were performed to investigate the effective fix ed charge concentration, X-f, and transport number of the ions, t(i), in th e membrane using two different procedures: keeping the concentration ratio constant, or keeping one concentration constant and changing the other one. Results show the membrane presents a weak cation-exchanger character, sinc e the following values were obtained: X-f = -(2.5 +/- 0.2) x 10(-2) M, t(K) = (0.56 +/- 0.06), t(Cl-) = (0.44 +/- 0.05); taking into account these va lues, concentration dependence of membrane potential was predicted. Membran e electrical resistance, R-m, was obtained from Impedance Spectroscopy (IS) measurements using equivalent circuits as models, and the membrane porosit y [Theta] = (0.11 +/- 0.02)% was also obtained from resistance values, whic h agrees very well with the value determined from geometrical parameters. F rom R-m, Delta phi(m) and Theta values, the diffusion coefficient of the io ns in the membrane pores can be calculated, and the following average value s were obtained: [DK+] = (1.9 +/- 0.4) x 10(-9) m(2)/s and [DCl-] = (0.8 +/ - 0.2) x 10(-9) m(2)/s, but for an average concentration higher than 0.06 M , their values do not differ practically from solution in agreement with th e small negative charge previously indicated. (C) 2000 Elsevier Science B.V . All rights reserved.