The pertrurbed-hard-chain theory (PHCT) for molecules interacting with spherically symmetric forces has been modified and extended to include anisotropic (multipolar) interactions. The anisotropic perturbation expansion of Gubbins and Twu is used in combination with lattice theory, with the assumption that the molecules are effectively linear. The original fourth-order perturbation with square-well potential used in the PHCT is replaced by a second-order perturbation of the Lennard-Jones potential. The resulting equation of state, the perturbed-anisotropic-chain theory, is applicable to simple as well as large polymeric molecules with or without anisotropic interactions. The new equation has been applied to pure fluids having substantial quadrupole moments and their mixtures. Mixture properties can be predicted accurately from pure-component properties alone and can be fitted within experimental uncertainty with small values of a binary interaction parameter.

A simple analytical equation for chainlike molecules interacting with square-well potential is derived by replacing the complicated attractive term in the perturbed hard chain theory (PHCT) of Beret, Donohue, and Prausnitz with a theoretical but simple expression derived by Lee, Lombardo, and Sandler. The resulting simplified perturbed hard chain theory (SPHCT) reproduces both experimental vapor pressure and liquid density data for a number of fluids over a wide temperature and pressure range with good accuracy.The three pure-component parameters in the SPHCT have been obtained for several n-alkanes and multipolar fluids. Average errors in predicted vapor pressures and liquid densities, over a wide temperature and pressure range, are about 3 and 4%, respectively. Preliminary mixture calculations indicate that the SPHCT predicts K factors and Henry's constants with reasonable accuracy without the use of any binary parameters.

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The associated perturbed-anisotropic-chain theory (APACT) has been applied to treat multicomponent mixtures, in which components exhibit Lewis acid-base interactions. Mixtures of amphoteric molecules (such as alcohols), acidic molecules (such as chloroform), and basic molecules (such as ketones) as well as nonassociating components (diluents) are treated. The acid-base version of the perturbedanisotropic-chain theory (ABPACT) is a closed form equation of state that takes into account explicitly dispersion interactions, polar interactions, and hydrogen bonding interactions between components that self-associate or solvate. The equation fits binary VLE mixtures quite accurately. Calculated results also are compared with those obtained from the Peng-Robinson equation of state, UNIFAC and the original APACT. In all cases where there are mixtures of associating components, the ABPACT gives a better fit of experimental data than these other equations.

The glassy polymer lattice sorption model (GPLSM) is a lattice-based activity coefficient model that has been developed for gas sorption in glassy polymers. The model recognizes the presence of holes on the lattice and determines how the number of holes changes by taking into account swelling due to penetrant gas molecules. The GPLSM equation has a composition-dependent energy term similar to that in the Flory-Huggins theory and an entropic term based on the mixing of gas molecules and holes. The utilization of sorptive dilation data for the determination of the number of holes gives a physically realistic interpretation of the local free volume in a glassy polymer. A good representation of the experimental data is obtained for the carbon dioxideand methane-polycarbonate systems.