Capillary column inverse gas chromatography (CCIGC) is a powerful tool to determine solubility and diffusion for a variety of polymer-solvent systems. The goal of this work was to determine solubility and diffusion of a toluene-copolymer system as a function of the polymer film thickness in a temperature range starting above the glass transition temperature, Tg, of the copolymer down to below the Tg of the copolymer. The purpose was to evaluate any influence of the polymer film thickness on the partition coefficient, K, or the diffusion coefficients, Dp. Four open tubular capillary columns were coated with the polystyrene-polyethylene copolymer, applying film thicknesses of 0.1, 2.0, 3.4, and 6.0 ?m, and measurements in the temperature range of 100 to –10°C were conducted.
Plotting the resulting partition coefficients as a function of reciprocal temperature showed the following: The classical S-shape for film thicknesses 2.0, 3.4 and 6.0 ?m. An S-shape or a linear dependency through the Tg of the polymer for a film thickness of 0.1?m, depending on the interpretation of the experimental data.
Diffusion coefficients as a function of reciprocal temperature were fitted using the free-volume model of Duda and Vrentas above Tg for film thicknesses 2.0, 3.4 and 6.0 ?m. Below the Tg, the Dp values diverged from the expected behavior. Again the 0.1?m showed either the same behavior as the thicker film columns, or a linear dependency through the Tg, depending on the interpretation of the data. In general, the Dp values were almost two magnitudes lower than the Dp values of thicker film columns over the whole temperature range.