Electrical conductivity enhancement of polyaniline by refluxing

The room temperature electrical conductivity of polyaniline (PANI) was found to increase remarkably after it was heated in tetrahydrofuran (THF) with refluxing for a certain period and then doped with methanesulfonic acid (MSA). The enhanced electrical conductivity of PANI was attributed to a partially cross-linked network generated via the formation of new chemical bonds between adjacent PANI chain segments during thermal treating, which may shorten the inter-chain distance and facilitate inter-chain transition of charge carriers in doped PANI. During the refluxing, the moderate dissolving power for PANI as well as a much lower boiling point of THF were considered to have a unique effect on the formation of such partially cross-linked network in PANI. As a comparison, PANI treated in poor solvents like methanol (or ethanol) and PANI treated in dimethyl formamide (DMF), which is a better solvent than THF but has higher boiling point, did not show an obviously increased electrical conductivity. Study on X-ray diffraction (XRD) analysis of PANI after refluxing showed that crystallinity decreased gradually with the increase of cross-linking degree, but the inter-chain cross-linking probably occurred first in crystalline region and then in the amorphous region. Electrical conductivity of PANI decreased after it was refluxed with THF for an extended period due to the decreased crystallinity and doping in PANI.