THE EFFECT OF PH ON POLYMERIZATION AND VOLUME CHANGE IN PPY(DBS)

Polymerization and electrochemically induced volume change in polypyrr ole doped with the large aromatic surfactant anion dodecylbenzenesulfo nate, PPy(DBS), were studied as a function of pH in unbuffered aqueous solutions prepared by mixing DBS acid and NaOH. Volume change was mea sured during the first, anomalous reduction and in subsequent cycles u sing a bending bilayer. The results differed completely from those obt ained by others for PPy doped with small, mobile anions. Films could b e deposited potentiostatically at all nominal pH values between 1 and 11, but growth was fastest at the lowest pH and uneven above pH 10 due to impaired nucleation. However, during potentiodynamic polymerizatio n, deposition and redox were easier at alkaline pH, having a smaller p eak separation and greater charge density. At pH less than 3, there we re no reduction or oxidation (redox) peaks and the films became insula ting. Contrary to expectations,;the pH of the growth solution did not affect the performance of the bilayer actuators, but the pH of the cyc ling solution was important. Bending was fastest in alkaline solutions , although the degree of bending was the same at low and high pH. Exce pt at very low pH, two pairs of redox peaks could be distinguished in the cyclic voltammograms, with volume change restricted to the lower p otential pair associated with Na (+) movement. There was no volume cha nge associated with the anomalous current peak seen during the first r eduction scan, regardless of pH, but the films contracted during re-ox idation. Thereafter, during reduction the films expanded to their orig inal, as-grown volume. (C) 1998 Elsevier Science Ltd. All rights reser ved.