A New Activity Model for Polymer Solutions in the Frame of Lattice Theory

Abstract

A simplified activity model for polymer solutions is derived from the Gibbs-Helmholtz relation, in conjunction with the lattice theory in this work. The model includes not only combinatorial and residual terms but also a free-volume (FV) term. The calculated results differ significantly between the model equations with and without taking the FV effect into consideration. The validity of this new method is demonstrated by comparing the calculated activities from the proposed model equation with those by the Entropic-FV (EFV), UNIFAC-FV, and UNIFAC methods. The overall average absolute deviation (AAD) of solvent activities in 34 polymer solutions was 7.58% for the EFV method, 5.32% for the UNIFAC-FV method, 22.00% for the UNIFAC method, and 3.48% for the proposed model. It is shown that the new model can yield improved results over the other models and is able to predict the phase behavior for polymer solutions over a wide range of molecular weights, temperatures, and densities.

Vapor–liquid equilibrium of copolymer+solvent mixtures: Thermodynamic modeling by two theoretical equations of state

“…West et al [16] used the single Sanchez-Lacombe lattice fluid equation of state to model both phases for a polymer-supercritical fluid-cosolvent system in a wide pressure range both volumetric and phase equilibrium properties for a cross-linked poly(dimethyl siloxane) phase in contact with CO 2 modified by a number of cosolvents. Liu and Cheng [17] used a simplified activity model for polymer solutions derived from the Gibbs-Helmholtz relation, in conjunction with the lattice theory to model polymer solutions. Vanderzande [18] made a complete study in his book about lattice models in polymer solutions.…”