In situ ellipsometric studies on the electrochemically induced structural modifications during poly(3-methylthiophene) formation

Aiming to investigate the influence of the growth potential on the properties of poly(3-methylthiophene), electrochemical and ellipsometric signals, simultaneously recorded during the potentiostatic polymer formation on platinum electrodes, are analysed. The experimental data is contrasted to that obtainable with the use of the three-layers model for the growth of homogeneous films. The results reveal that the polymer prepared at 1.36 V (versus SCE) shall be regarded as a multilayered material, whereas the polymer synthesized at 1.38 V (or higher potentials) can be modelled as a two layered system. For all studied growth potentials, the outer layers are less dense. Differences in the growth process imparted by small variations in the applied potential are also clearly retrieved from the calculated complex refractive indices: the inner layers of the films obtained at low growth potentials are thicker, less absorbing and displaying higher optical density. These features correlated with the amount of charge spent prior the polymer deposition at each potential support the precipitation of oligomers of distinct length originating differently ordered polymer structures. The analysis of the redox behaviour displayed by the films prepared under different controlled potentials is also consistent with the interpretation of the ellipsometric results.