Pressure dependence of the resistance in polyaniline and its derivatives at room temperature

We report on our high pressure measurements on powdered, doped samples of polyaniline (PAN), poly-o-toluidine (POT), poly-o-ethylaniline (OPEA) and poly-o-propylaniline (OPPA) at room temperature using a diamond anvil cell up to 22 GPa. Since the primary influence of pressure is sample compression, application of pressure leads to an initial decrease in the resistance (enhanced conductivity) indicating greater interchain coherence due to reduced interchain separation. The resistance of our samples as a function of pressure depends on the interplay between increased interchain transfer due to increased pressure and decreased transfer rate due to smaller localization length. Higher values of the resistance at ambient pressure as the substituent group along the main chain PAN backbone gets larger is consistent with measurements of dc conductivity on the same samples.