Voltammetric study of the reduction and relaxation of poly(o-toluidine). Effect of the polymer thickness and the external electrolyte nature and concentration

Swelling and volume changes of polyaniline upon redox switching

“…This suggests that the cause for the volume increase is some change in the polymer itself, more likely a conformational change due to the formation of quinoid structures. This should not be a full coil/planar transformation, since several studies [30,31] indicate that such transformation takes place after full relaxation at the lower limit. However, some degree of conformational change should occur during the stationary cycling, when the quinoid rings develop, in the positive scan, and disappear, in the negative scan.…”

“…When the electrode was placed in the monomer-free electrolyte, the potential was cycled continuously at v ¼ 0:012 V s À1 until a stationary voltammogram was obtained. Then, the potential was held at the lower limit, E ¼ 0:1 V, for time intervals long enough for the polymer to be fully reduced (dedoped) and relaxed [31]. Afterwards, the potential sweep was started, recording the voltammogram and the images simultaneously, until a stationary voltammogram was again obtained.…”

“…There are several studies [30,31,36], which show that, during the full reduction and relaxation at the lower limit, some form of conformational transition, such as planar-coil, takes place. Also, such transitions have been related to other processes such as secondary doping [49,50].…”

“…More recently, a preliminary study conducted on poly(2-methylaniline), a material similar to PANI, in 1 M acid solutions has shown volume changes upon redox switching which are dependent on the electrolyte anion, and showing a first cycle effect when the polymer is fully reduced and relaxed [30]; the results were interpreted in terms of two processes in different time scales, the faster one being the exchange of ions and water with the external solution (namely swelling/deswelling), and the slower process a conformational change of the polymer backbone. Here, the polymer is termed ''fully reduced and relaxed'' in the sense given in [31]. That is, fully reduced when, after holding the potential at negative values in the insulating region, the charge of the first anodic peak does not increase further when the holding time increases, and fully relaxed when the first anodic peak shows no further changes either in the peak potential or in the peak width at half height with further holding.…”

“…Different acidic media (H 2 SO 4 , HClO 4 and HCl) were employed in order to assess the influence of acidity and the anion of the electrolyte solution. The volume changes accompanying the so-called ''first cycle or relaxation effect'' [31,35,36] in the sense given above, were studied, as well as those occurring during stationary cycling. The volume changes were measured with the aid of an image capture and processing system.…”