Modeling Sorption Behavior for Ethanol/Water Mixtures in a Cross-linked Polydimethylsiloxane Membrane Using the Flory-Huggins Equation

Abstract

The sorption behaviors of aqueous ethanol solutions in a polydimethylsiloxane (PDMS) membrane at 25°C were investigated in this study. The sorption isotherms for the ethanol and water binary mixtures were experimentally determined. The water uptake reached a maximum at a concentration of 80 wt% ethanol, and the partial water uptakes were even higher than the pure water solubility for 10–95 wt% ethanol solutions in the PDMS membrane, which implies the presence of a strong synergistic effect due to the ethanol copermeant. The Flory-Huggins equation was utilized to predict the sorption levels at various ethanol/water compositions. The binary Flory-Huggins interaction parameters obtained from pure solvent sorption experiments (χ_iM ) and the ethanol/water vapor liquid equilibrium data (χ ₁₂) were used in the construction of the model for predicting the partial penetrant solubilities. Using constant χ_ij parameters could not render satisfactory predictions; therefore, concentration-dependent expressions for either χ ₁₂ or χ_iM were employed to improve the prediction power. We found that constant or concentration dependent χ ₁₂ parameters had little impact on the predicted sorption, whereas the modified concentration-dependent χ_iM values greatly improved the modeling precision.

Keywords:

• ethanol/water solutions
• Flory-Huggins equation
• polydimethylsiloxane (PDMS)
• sorption modeling

Acknowledgments

The authors acknowledge the financial support from Chang Gung University (BMRP326) and the National Science Council of Taiwan (NSC 99‐2221-E-182‐005).