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 Hen ry's law concentration region by inverse gas chromatography (IGC). Lin ear adsorption isotherms were constructed for n-hexane, n-heptane, n-o ctane 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 dat a 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 coeffici ents calculated for n-alkanes increased with increasing chain length o f the probe molecule and decreased with increasing temperature. Thermo dynamic parameters were indicative of strong interaction between n-alk anes and polystyrene, with the standard free energy (DELTAG(A)0) incre asing with increasing chain length of probe. From the free energy of a dsorption per methylene group, the London dispersion force contributio n to the polystyrene surface free energy was estimated as 60.8 mN/m. I t is concluded that this method can be applied to amorphous polymers s uch as polystyrene, at effectively zero coverage, if experimental cond itions are carefully chosen so as to minimize penetration of the probe molecules into the bulk of the polymer.