Electrical conductivity transitions and self-assembly in comb-shaped complexes of polyaniline based on crystallization and melting of the supramolecular side chains

We report self-assembly and electronic conductivity transitions in polyaniline (PANI) where the iminic nitrogens are protonated by sulfonic acid-terminated low molecular weight poly(ethylene oxide) CH₃−(O−C₂H₄−)₄₆−CH₂−SO₃H (PEOSA), i.e., which contains 46 ethylene oxide repeat units. The complex PANI(PEOSA)_0.5 self-assembles due to the comb-shaped architecture consisting of the PANI backbone and the supramolecular PEO side chains, as characterized using small- and wide-angle X-ray scattering (SAXS and WAXS) and transmission electron microscopy (TEM). PEO in the complex PANI(PEOSA)_0.5 is crystalline near room temperature; TEM and SAXS indicate lamellar self-assembly with a long period of ca. 150 Å, and the conductivity is of the order 10^-4 S/cm. A collapse of the self-assembly periodicity to 115 Å is observed at ca. 55 °C during a slow heating at 1 °C/min, and the conductivity drops stepwise to ca. half of the value as the PEO chains melt. Even if the observed conductivity transition is still relatively small, it is reproducible and reversible upon heating and cooling, with some hysteresis. We expect that the concept can be developed to open new possibilities for responsive conjugated polymers.