FINITE CONCENTRATION INVERSE GAS-CHROMATOGRAPHY - DIFFUSION AND PARTITION MEASUREMENTS

Inverse gas chromatography (IGC) is a very fast, accurate, and reliabl e technique to measure diffusion coefficients. This technique however, has been limited to measurements in the infinite dilution region, i.e ., in the region of negligible amount of solvent in the polymer. We ha ve extended the scope of inverse gas chromatography to measure diffusi on coefficients at finite concentrations of the solvent. This involves doping the carrier gas with a solvent of interest to achieve finite c oncentrations of solvent in the carrier gas and hence in the polymer. The carrier gas is passed through a saturator maintained at constant t emperature to achieve this purpose. Diffusion coefficients for polyvin yl acetate-toluene, and polystyrene-toluene systems were determined at finite concentrations. The results were compared with the traditional gravimetric sorption and piezoelectric sorption measurements reported in the literature. The data are in excellent agreement with the value s reported, correlate well with the Vrentas-Duda free volume theory, a nd can also be predicted from infinitely dilute data using the free vo lume theory. (C) 1997 John Wiley & Sons, Inc.