Effects of ultra-high pressures (>3.6 GPa) on the electrical resistance of polyaniline by in situ FT-IR studies

Electrical resistance measurements and FT-IR spectroscopy of polyaniline were studied in situ under ultra-high pressures generated by a diamond anvil cell (DAC). The electrical resistance of polyaniline decreased as the pressure increased, exhibiting polaron conductor characteristics. Minimum electrical resistance was observed at 3.6 GPa, about three orders of magnitude smaller than that at 1.0 GPa. Changes in electrical resistance were reversible when the pressure was below 3.6 GPa. In situ FT-IR results showed that irreversible chemical changes of the quinoid units in polyaniline molecular chains took place when the pressure exceeded 3.6 GPa, giving rise to a huge increase in electrical resistance.