Multicomponent polymer/solvents equilibria: An evaluation of Flory-Huggins theory for crosslinked PDMS networks swelled by binary mixtures

The prediction of equilibrium volume fractions of solvents mixtures in a polymer network is of utmost importance for processes dealing with polymeric materials (e.g. chromatographic and membrane processes). Up to now, few studies have studied the ability of existing theories to predict experimental multicomponent sorption data in polymers; this work intends to achieve that purpose on model liquid mixtures in contact with silicone rubber (polydimethylsiloxane). The equilibrium volume fractions of three liquid mixtures (chloroform/toluene; ethanol/toluene; ethanol/2-butanol) in crosslinked PDMS samples have been determined experimentally at 40 degrees C. Results are compared to predictions by the Flory-Huggins theory applied to ternary mixtures (one polymer and two liquids) with constant interaction parameters and negligible elastic contribution. Solvent/polymer interaction parameters have been determined by swelling the crosslinked samples in pure liquids, while liquid/liquid interaction parameters have been estimated from liquid/vapor equilibrium data It is shown that the Flory-Huggins theory offers good predictions in the case of good (chloroform, toluene) and fair (2-butanol) PDMS solvents, while significant discrepancies are obtained with a non solvent (ethanol). Implications in ternary diagrams simulation and possible prediction improvements, based on non constant interaction parameters, are discussed.