Mesostructures of polyaniline films affect polyelectrochromic switching

The dynamics of polyelectrochromic switching in films of polymer-acid-doped polyaniline (PANI) having different internal film structures - and thus different extents of exposed surface area - was investigated. We present a simple model that captures the influence of PANI's mesostructure on its transitions between the insulting and conducting states. Films possessing high internal surface areas exhibit longer electrochromic switching times relative to films with low exposed surface areas. By homogenizing the mesostructures via solvent-induced structural relaxation of PANI thin films, the polyelectrochromic response of PANI hastens and differences are eliminated. This solvent-induced structural relaxation effectively increases the extent of percolation of conductive pathways, resulting in shorter electrochromic switching times as PANI transitions from insulating to conductive states. Increasing the size of the buffer cation also results in longer switching times in mesoscopically heterogeneous films. Following structural relaxation and homogenization, the influence of the buffer cation on polyelectrochromic switching kinetics is eliminated. These correlations point to the importance of internal film structure in electrochromic switching of conducting polymers, and provide insights for the design of next-generation electrochromic polymer systems.