Meta-analysis of critical points to determine second virial coefficients for binary biopolymer mixtures

Abstract

A method is introduced to extract virial coefficients from phase diagrams. Previous work demonstrated that the critical point of a phase diagram (two parameters) of a binary polymer mixture provides too little information to allow a full description of the phase diagram when using the Edmond-Ogston model (which requires three parameters). In this paper, it is shown that simultaneous analysis of multiple phase diagrams of binary polymer mixtures with shared components does allow the extraction of virial coefficients. The method is illustrated by analyzing phase diagrams for various polymer mixtures directly available in literature. The obtained virial coefficients for the polyethylene oxide/polyethylene glycol (PEO) and dextran polymers are compared to values as obtained by membrane osmometry and shown to be in satisfactory agreement. These virial coefficients are shown to follow a power-law dependence on the molecular weight. In addition, it is observed that the cross-virial coefficient can be approximately described by a simple mixing rule. This rule makes it possible to estimate the phase diagrams for polymer mixtures, where the virial coefficients of the pure components are known, but the cross-virial coefficient is unknown. The method to extract virial coefficients is also applied to a number of mixtures containing agarose, bovine serum albumin or gelatin, mixed with either PEO or dextran. The virial coefficients obtained in a simultaneous fit involving fitting the critical points of multiple phase diagrams are used to calculate the full original individual phase diagrams. Generally, there is good agreement between such a calculated phase diagram and the original experimental phase diagrams.