THE ADSORPTION OF HYDROCARBONS ON POLYSTYRENE BY INVERSE GAS-CHROMATOGRAPHY - INFINITE DILUTION CONCENTRATION REGION

The adsorption of some n-alkanes on polystyrene was studied in the Henry's law concentration region by inverse gas chromatography (IGC). Linear adsorption isotherms were constructed for n-hexane, n-heptane, n-octane and n-nonane at 30-degrees and additionally for n-heptane at 40, 50 and 60-degrees. The BET equation was applied to the adsorption data and the specific surface area of the polystyrene coated glass beads was estimated. Surface areas found by IGC were in good agreement with those found by nitrogen adsorption at -196-degrees. Partition coefficients calculated for n-alkanes increased with increasing chain length of the probe molecule and decreased with increasing temperature. Thermodynamic parameters were indicative of strong interaction between n-alkanes and polystyrene, with the standard free energy (DELTAG(A)0) increasing with increasing chain length of probe. From the free energy of adsorption per methylene group, the London dispersion force contribution to the polystyrene surface free energy was estimated as 60.8 mN/m. It is concluded that this method can be applied to amorphous polymers such as polystyrene, at effectively zero coverage, if experimental conditions are carefully chosen so as to minimize penetration of the probe molecules into the bulk of the polymer.