Evaluation of the electrochemical characteristics of a poly(vinyl alcohol) poly(acrylic acid) polymer blend

The polymer blend poly(vinyl alcohol)/poly(acrylic acid) (PVA/PAA) has been evaluated as a coating on graphite electrodes. The uptake of tris(2,2'-bipyridyl)ruthenium(II), Ru(bpy)(3)(2+), by the film was monitored by cyclic voltammetry and was found to be pH dependent. A plot of current response versus pH is analogous to a titration curve of a mixture of acids with pK(a) values in the range of 4-6. At pH 1 where the PVA/PAA film is neutral, voltammograms of Ru(bpy)(3)(2+) were comparable to ones recorded at a bare electrode. At pH 7, where the film is anionic because the carboxyl group is deprotonated, a current enhancement factor of 9 to 16 compared to a bare electrode was obtained. This pH-dependent behavior is also observable for plots of the peak separation versus pH in which E-p of cyclic voltammograms increases with pH. The effect of different supporting electrolytes was investigated by measuring the current response with LiNO3, NaNO3, and KNO3 over a range of pH. Cyclic voltammograms of Fe(CN)(6)(3-) showed that negatively charged species are rejected by the polymer film. (C) 1988 Elsevier Science Ltd. All rights reserved.