An equation of state for polymers and normal fluids using the square-well potential of variable well width

A perturbation theory equation of state for mixtures of freely jointed squa re-well fluids of variable well width that takes into consideration the inf luence of the attractive part of the intersegment potential on the chain pr operties is applied to describe thermodynamic properties of pure normal flu ids, polymers, and their mixtures. The equation of state is based on second -order Barker and Henderson perturbation theory to calculate the thermodyna mic properties of the reference sphere fluid and on first-order Wertheim th ermodynamic perturbation theory to account for the connectivity of spheres to form chains. Pure polymer parameters are determined from low molecular w eight pure substance parameters, from pure polymer volumetric data, and fro m mixture data. Good results are obtained when this equation of state is us ed in the calculation of vapor-liquid equilibrium data of highly asymmetric mixtures, with polymer properties determined from low molecular weight sub stance properties, molecular weight and temperature-independent parameters, and no binary adjustable parameters.