Ions transport and self-doping in layer-by-layer conducting polymer films

The self-doping mechanism for charge transport is investigated in layer-by-layer (LBL) films from two conducting polymers, namely poly(o-methoxyaniline) (POMA) and poly(3-thiophene acetic acid) (PTAA). The efficiency of charge intercalation, defined as the ratio between the charge and the mass change, is twice for the POMA/PTAA LBL film in comparison with a cast POMA film. This is attributed to differences in the diffusion-controlled charge and mass transport, where distinct ionic species participate in the LBL films, as demonstrated with experiments using a quartz crystal microbalance. The doping efficiency for LBL film is the same, i.e., 3.93 × 10−4 and 3.56 × 10−4 g/C for the Li+ and (C2H5)4N+ doped films, and is different for the cast POMA film, i.e., 11.3 × 10−4 for Li+ and 6.45 × 10−4 g/C for (C2H5)4N+. Therefore, once no significant differences in the intercalation mechanism are observed when different cations, Li+ or (C2H5)4N+, are used with the LBL films, this indicates that the self-doping mechanism is controlled by the exchange of anions.