Prediction of Water Solubility in Glassy Polymers Using Nonequilibrium Thermodynamics
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abstract
In this study, the sorption of water in poly(methyl methacrylate) (PMMA) was measured at various water vapor activities (0-0.85) at 25, 35, and 45 C using a quartz spring microbalance. Furthermore, the water sorption isotherms in PMMA were predicted using two nonequilibrium thermodynamic models: the nonequilibrium lattice fluid (NELF) model and nonequilibrium statistical associating fluid theory (NE-SAFT), where excellent agreement between the NE-SAFT prediction and experimental data was observed. In contrast, deviation between the NELF model prediction and water sorption isotherms in PMMA was observed above a water activity of ca. 0.50. In situ time-resolved Fourier transform infrared attenuated total reflectance spectroscopy confirmed the presence of self-associated water (i.e., water clusters) at elevated water activities, providing a rationale for deviation between the NELF model and experimental data, where unlike NE-SAFT, the NELF model does not account for these self-association interactions. The NE-SAFT model prediction was extended to five additional glassy polymers, including poly(lactide), poly(acrylonitrile), poly(ethylene terephthalate), poly(vinyl chloride), and poly(styrene), where good agreement between the model predictions and water sorption isotherms was also observed. Additionally, a correlation between the polymer segment number and water solubility was observed. 2013 American Chemical Society.
