Surface and thermodynamic characterization of conducting polymers by inverse gas chromatography. I. Polyaniline.

The surface thermodynamic characteristics of both doped polyaniline (PANI-HEBSA) and the non-conducting form (PANI-EB) were investigated using inverse gas chromatography. Fourteen solutes were injected into two separate chromatographic columns containing PANI-EB and PANI-HEBSA. All solutes interacted strongly with the conducting form PANI-HEBSA; in particular, undecane and dodecane showed stronger interaction due to the increase of the dispersive forces. Methanol and ethanol showed stronger H-bonding with the conducting form than propanol and butanol. A curvature was observed for acetates and alcohols with a maximum of around 145 degrees C as an indication of a phase change from a semicrystalline to amorphous phase. DeltaH(l)s value increased considerably (-3.35 to -46.44 kJ/mol) while the deltaH(l)s for the undoped PANI (PANI-EB) averaged about -0.03 kJ/mol. PANI-EB-alkane interaction parameters were measured and ranged from +0.40 to +1.50 (endothermic). However, PANI-HEBSA showed an exothermic behavior due to the polar surface (-1.50 to +1.2). Interaction parameters decreased as the temperature increased and are characteristic of the strong interaction. The dispersive surface energy of the non conducting PANI-EB ranged from 29.13 mJ/m2 at 140 degrees C to 94.05 mJ/m2 at 170 degrees C, while the surface energy of the conducting PANI-HEBSA showed higher values (150.24 mJ/m2 at 80 degrees C to 74.27 mJ/m2 at 130 degrees C). Gamma(s)d values for PANI-EB were found to be higher than expected. The trend of the gamma(s)d change direction is also surprising and unexpected due to the thermal activation of the surface of the polymer and perhaps created some nano-pores resulting in an increase in surface energy of the non-conducting form.