Evaluation of the surface properties of poly(ionic liquid) materials by inverse gas chromatography

Inverse gas chromatography (IGC) was used as a tool to evaluate the surface parameters of three poly(1-alkyl-3-vinylimidazolium hexafluorophosphate) (P[CnVIM](PF6], n = 2, 4, 6) materials that were obtained by a freeradical polymerization. IGC characterization was carried out at temperatures ranging between 303.15 and 343.15 K for determining the dispersive free energy (gamma(d)(s)) as well as the Lewis acidity and basicity parameters of the three materials. The retention behaviour of the probes on the surfaces of the three materials was analysed by plotting the net retention volumes (V-n) of the probes as a function of temperature. The dispersive free energy results revealed that all three materials have high gamma(d)(s) values and that the gamma(d)(s) value decreases in an almost linear fashion with increasing temperature. The acid-base data for the three materials confirmed that the surfaces of all three materials can be considered to be amphoteric with a predominantly basic character and that the basicity decreases with increasing alkyl side chain length on the imidazolium backbone.