Characterization of a poly(3-methyl thiophene) film by an in-situ dc resistance measurement technique and in-situ FTIR spectroelectrochemistry

The newly developed in-situ dc resistance measurement technique called the contact electric resistance (CER) technique as well as in-situ external reflectance FTIR spectroscopy were applied for studying the conductivity and redox behaviour of poly(3-methyl thiophene) (PMeT) in acetonitrile and aqueous solutions. The maximum conductivity as well as the effect of the thickness of the film on the evolution of the conductivity were observed to depend on whether the PMeT films are electrochemically synthesized and studied in the presence of Bu4NClO4 or Bu4NPF6 in acetonitrile.
The maximum conductivity was 10−2 S cm−1 for the former and 10−1 S cm−1 for the latter system. The deactivation of PMeT began in acetonitrile solutions at about 1.4 V. In accordance with this the in-situ IR spectra showed that the number of (bi)polarons started to decrease.
The aqueous solutions were observed to decrease the maximum conductivity by 2–3 decades depending on the anion and to cause a much slower resistance response to an applied potential when compared with the results in acetonitrile.
The FTIR measurements proved that in aqueous solution (bi)polarons similar to those observed in acetonitrile are formed in the film during anodic oxidation.
The CER technique was found to be well suited for measuring the in-situ resistance of conducting polymers.