Characterization of surface thermodynamic properties of p-toluene sulfonate-doped polypyrrole by inverse gas chromatography

Summary p-Toluene sulfonate-doped polypyrrole (PPyTos) powder has been characterized by inverse gas chromatography at various temperatures. We have used apolar n-alkanes and polar probes of differing acidity and basicity to interrogate the London dispersive and Lewis acid-base properties of PPyTos, respectively. We have found that the London component of the surface energy (γs^d) is about 90 mJ · m⁻² at 25°C and the acid-base contribution to the free energy of adsorption (ΔG_a ^AB) for Lewis bases is higher than 8 kJ · mol⁻¹. These results show that PPyTos is a high energy material and is capable of very strong specific acid-base interactions. Lewis acidity is, however, dominant and is shown to increase with temperature. The determination of the heats of adsorption for tetrahydrofuran and ethyl acetate enabled us to determine Drago’s E_A, C_A, E_B and C_B parameters. Whilst E_A and C_A are similar to those published for chloride-doped polypyrrole and rank PPyTos as a hard acidic species, the E_B and C_B values suggest that PPyTos is a very soft Lewis base.