ELSEVIER Synthetic Metals 101 (1999) 90-91 Solution aging effects on the poly(3-methylthiophene) electrochemical properties A. A. Correa and E. C. Pereira Laboratho interdisciplinar de Eletroquimica e Cerkmica Departamento de Quimicu - Universidade Fideral de So Carlos - C.P.: 676 - 13.560-970 - Sio Cat& - SP - Bra& e-mail: decp@power. ufscar. br Abstract The effect of multiple polymerizations of poly(3-methylthiophene) using the same solution on its electrochemical properties was systematically investigated. After each polymer preparation. using always 475 mCcm“ of formation charge, the electrochemical behavior of the films was investigated with cyclic voltammetry. It was observed a decrease in the current density during the polymer growth, in the current density peak and a displacement of the anodic peak potentials to more positive values of the voltammetric curves. These effects could be associated with a variation in the nucleation process which modify the polymer properties as the preparation solutions are used several times. KeJqvords: electrochemical polymerization. electrochemical methods, polythiophene and derivatives The objective of this work is to investigate the aging of the solution when several polymerizations are made in the same solution. Chronoamperometry was used to study the differences among the growth curves, and the electrochemistry characterization of the polymer films was made through cyclic voltammetry. It will also be analyzed the influence of others variables, such as: electrolyte type. monomer concentration and temperature in the polymerization. Factorial design was used to calculate the effects of the polymerization variables [I]. The usefulness of factorial design is that, having selected the important variables it is possible to evaluate quantitatively its responses. Beyond the responses. using this method, its possible to measure if the variables are dependent. that is. if the value of one variable affects the response of a second variable. The execution of a factorial design consists of accomplishing the experiments in all the possible combinations of the factors mvolved in the system in its different levels. The responses. that are, in this case. the current density anodic peak. were obtained through matrix calculation by the combination among the different factors. For synthesis of the polymer it was used a one cell compartment and three electrodes, being as working electrode a platinum disk ( A= 0.2 cm’), as auxiliary electrode a platinum plate and as reference electrode a silver wire. The poly(3- methylthiophene) films were prepared at constant potential, E=1.515 V in acetonitrile solution under different preparation conditions. The polymer characterization were made by cyclic voltammetry in acetonitrile solution containing the same electrolyte used in the polymerization. All measurements were made in a potenciostat-galvanostat EG&PARC model 273. It was used factorial design to estimate the effects of the preparation variables. The preparation variables, called of factors, are: type of electrolyte, monomer concentration and temperature. and the levels are the different possibilities for a same factor. The variables of level - are: LiC104, 0. IM of monomer concentration and 5’C; and the level + are: NaBF,, 0.2M of monomer concentration and 25’C. The minus sign represents the low level and the plus sign the high level of the factor. Seven polymer films were made in the same solution with each one of the eight preparations conditions. All the polymers were prepared using 475 mCcms2 of formation charge. Figure 1 exhibits typical curves for the polymer growth in same solution. Initially, the curves present a current peak followed by a current minimum and, finally, of a current increase. It was observed that the minimum current time displaces for higher values and the final current density decrease as the solution ages. The curves presented at Figure 1 show only the initial stage of the growth process. Figure 2 shows the voltammograms for the polymers prepared at the same solution. It was observed a decrense in the current density peak and a displacement of anodic peak potential to more positive values. 8- B- N- 5 4- E Y 2- o- I I 0 1 2 J- time(s) Figure 1: Current density anodic as function of time for the polymerization of the 3-methylthiophene. The measurements were made in O.lM LiC104 in acetonitrile. O.lM monomer concentration and T=25’C. 0379-6779/991$ - see front matter 0 1999 Elsevier Science S.A. All rights reserved. PII: so379-6779(98)01214-4