EQCM study of electropolymerization and redox cycling of 3,4-polyethylenedioxythiophene

Polyethylenedioxythiophene films were electropolymerized potentiostatically (E = 1.1-1.3 V/SHE) at a gold electrode covering an EQCM from solutions co ntaining monomer, lithium perchlorate and non-ionic surfactant (polyoxyethy lene-10-laurylether). The ion exchange was studied by EQCM during redox cyc ling at a scan rate of 20-50 mV s(-1) in 0.5 M LiClO4 + 0.5 M LiCl + 0.5 M Na toluenesulfonate solutions in the potential range - 0.5 < E < 0.8 V (SHE ). Mass versus charge curves display a hysteresis. During the reduction sca n the ion content of the film is in equilibrium and is defined by the poten tial, whereas during oxidation the mass lags behind the charge due to slow water exchange. The reduction scan can be described by equilibrium theory s upposing that about 40% of counter-ions remain bound in the film. During po lymerization at E greater than or equal to 1.2 V, the mass gain calculated from the frequency change slows down more rapidly than is estimated from th e current. This may be attributed to the viscosity of the growing film with acoustic decay length of 2.45 mum. (C) 2001 Elsevier Science B.V. All righ ts reserved.