Difference in doping behavior between polypyrrole films and powders

Abstract

The differences in protonation and charge transfer behavior between polypyrrole (PPY) powders and films doped with inorganic acids, such as H 2SO 4 and HClO 4, or bulky acids, such as dodecylsulfonic acid (DS), toluene-4-sulfonic acid (TSA), dodecylbenzensulfonic acid (DBSA) and poly(styrenesulfonic acid) (PSSA), were assessed quantitatively by the X-ray photoelectron spectroscopic (XPS) technique. PPY-dodecylsulfate and PPY-toluene-4-sulfonate films with [N +] [N] ratio over 40% can be readily prepared electrochemically. Treatment of these salt films with a base results in the 25% deprotonated PPY. Reprotonation of the 25% deprotonated PPY films (containing 25% =N- units) by excess bulky acids readily results in complexes with surface [N +] [N] ratios substantially above 50%. For deprotonated PPY films loaded with excess inorganic acids, and deprotonated PPY powders loaded with excess simple or bulky acids, the protonation level or [N +] [N] ratio remains in the order of 25 to 30%. Raman and UV-Vis spectroscopies show little difference in structures of PPY formed chemically and electrochemically, but morphologies of cross sections of the simple and bulky anion-doped samples look different from each other. The enhanced charge transfer interaction in PPY-bulky anion films is probably attributable to the counter-ion-induced molecular ‘blending’ between the polymer and the dopant.