Electrochemical Properties of Polythiophene (PTs) depending on Preparation Conditions

Electrochemical Properties of polythiophene (PTs) depending on preparation conditions

Introduction

The main feature of the conductive organic polymers such as polythiophene (PT) and polypyrrole is that they all contain “p” electron structure extending throughout their configuration. These polymers are generally insulators or semi-conductors in their undoped state but can be made as conductive as metals when they are subjected to a doping process. They are highly conductive in an oxidized state. The conductance process in these polymers is believed to take place by “electron delocalization”.

Organic polymers have very complicated morphological structures depending upon the method of synthesis. Therefore, their properties vary according to their structural features. It is very difficult to obtain the same material if the synthesis conditions are changed.

Here, X represents a hetero atom such as nitrogen or sulfur.

Imanishi et al. proposed a two-step mechanism for the polymerization of these monomers. According to their scheme, polymerization starts with the formation of a cation radical that is formed by a loss of an electron from the monomer. These radicals may either give substitution or combination reactions. The oxidation of thiophene is irreversible, which shows that the cation radical formed in the first step as depicted below is extremely reactive.

Electrochemical properties of PT films largely depend on the supporting electrolyte, especially on the anion type. This study concerns the behavior of PT films obtained in acetonitrile containing different Supporting electrolytes. Various research has been carried out upon this issue. In this study the effect of the supporting electrolyte was investigated with cyclic voltammetry supplemented by in situ conductivity measurements. The surface conductance studies carried with the in situ technique showed that it was possible to prepare PT films having different conductivities depending on synthesis conditions.

Experimental

The polymer was synthesized at constant potential and current using a Princeton Applied Research (PAR) 363 model potentiostat and galvanostat. The cyclic voltammograms were recorded by the same potentiostat coupled to a Wenking VSG8 Model scan generator. The scan rate was 20 mV/s. All syntheses were carried out in acetonitrile using tetrabutyl ammoniumperchlorate (Bt4NP), tetraethyl ammoniumtetrafluoroborate (Et4NBF4) and tetrabutyl ammoniumhexafluorophosphate (Bt4NPF6) supporting electrolytes. The supporting electrolytes were checked to ensure that they were not reactive in the potential range employed. All chemicals were Merck proanalysis grade and used without further purification.

The in situ resistance measurements were carried using a Tacussel bi-potentiostat in a manner similar to that employed by other workers where two different potentiostats or special circuits were used. The double electrode system (DES) necessary for the measurement was formed by putting a 0.05-cm thick PVC film between two 1.5×0.5×0.05 cm3 Pt plates, which were each soldered to a silver-coated copper lead. The copper leads were insulated from each other with Teflon bands. The system is embedded in a glass tube filled with bubble-free araldite. The system was kept at 100°C for 24 h to set the araldite. The bottom part of the tube was mechanically polished to a mirror finish.

The synthesis and the conductance measurements of the polymers were carried out ...