Electrochimica Acta 45 (2000) 3841 – 3850 Quartz crystal microbalance study of electrochemical deposition of poly(3-dodecylthiophene) films on Au electrodes Magdalena Skompska * Department of Chemistry, Uniersity of Warsaw, ul. Pasteur 1, 02 093 Warsaw, Poland Received 17 August 1999; received in revised form 5 November 1999 Abstract Poly(3-dodecylthiophene) films were synthesised electrochemically from a propylene carbonate solution of the monomer, by galvanostatic method and cyclic voltammetry. Electrochemical properties of the resulting polymers were compared with the properties of regioregular head-to-tail (HT) polymer synthesised chemically. The first part of the work is focused on the electrochemical characteristics of HT polymer, namely on dependence of the shape of cyclic voltammograms obtained for redox reaction of the polymer on the film thickness and mean conjugation length. In the second part, the optimum conditions of electrosynthesis have been established. The quartz crystal microbalance measurements carried out during potentiodynamic polymerisation of 3-dodecylthiophene (by cyclic voltammetry) showed that deposition of the polymer film was preceded by dissolution of the gold substrate. At the later stage of the film formation, the oligomers that were initially accumulated in the vicinity of the electrode, attained the crucial lengths and precipitated on the electrode surface. In the case of a slow diffusion of the monomer to the electrode the growing film may be irreversibly overoxidised or/and crosslinked. © 2000 Elsevier Science Ltd. All rights reserved. Keywords: Poly(3-dodecylthiophene); Electrodeposition; Electrochemical quartz crystal microbalance; Conjugation length; Oligomers www.elsevier.nl/locate/electacta 1. Introduction Poly(3-alkylthiophenes) (PATs) are a unique class of conducting polymers with good solubility, stability, processibility and electroactivity. A milestone step in the development of polythiophene was done by McCul- lough and Lowe [1] and Chen and Rieke [2], who elaborated the methods for the chemical synthesis of regioregular PATs. These methods allow obtaining head-to-tail (HT) regioregular or completely regioran- dom PATs as well as other regioisopolymers with a variety of percentages of regioregularity. Electrochemi- cal polymerisation yields PAT layers with relatively low amount of HT–HT couplings, i.e. 55% [3] but this method is still attractive because of its simplicity, rapid- ity and ability to control of degree of the polymer oxidation. Majority of the studies on electrochemical polymerisation of 3-alkylthiophenes was performed be- fore the procedure of regiocontrolled synthesis was provided [4,5]. According to Roncali et al. [4], the layers of best quality are obtained from acetonitrile solutions of 0.2 M monomer by means of galvanostatic method at current density between 0.5 and 10 mA cm -2 . The polymer layers, obtained at relatively low current densities were found to be inhomogeneous, with shorter conjugation length than those deposited at a current density between 5 and 10 mA cm -2 [4]. On the other hand, the results presented by Masuda et al. [6] showed that the poly(3-dodecylthiophene) films of the * Fax: +48-22-8225996. E-mail address: mskomps@chem.uw.edu.pl (M. Skompska). 0013-4686/00/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved. PII: S0013-4686(00)00457-6