(170b) Water Sorption and Diffusion in Glassy Polymers: Nonequilibrium Thermodynamics and States of Water

In this study, the sorption and diffusion of water in six different glassy polymers were investigated, including poly(methyl methacrylate), poly(lactide), poly(acrylonitrile), poly(ethylene terephthalate), poly(vinyl chloride), and poly(styrene). Sorption and diffusion were measured at different temperatures, over a wide range water vapor activity, using both gravimetric and spectroscopic techniques; including quartz spring microbalance (QSM) and in situ time-resolved Fourier transform infrared-attenuated total reflectance (FTIR-ATR) spectroscopy. Specifically, two nonequilibrium thermodynamic models: the nonequilibrium lattice fluid (NELF) model and the nonequilibrium statistical associating fluid theory (NE-SAFT) were employed to predict water solubility in these glassy polymers, where excellent agreement between the NE-SAFT predictions and experimental data was obtained over the entire water vapor activity range explored. Furthermore, the states of water in these glassy polymers were analyzed using the Zimm-Lundberg clustering theory, as well as in situ FTIR-ATR spectroscopy, where the latter technique provides a direct, molecular-level measurement of the states of water in the polymer through distinct infrared bands. Surprisingly, contrasting physical pictures of the states of water were observed in these glassy polymers when comparing the Zimm-Lundberg theory to the infrared spectroscopy results. Finally, the infrared spectroscopy results were compared to temperature-dependent diffusivity data to help elucidate the impact of the states of water on sorption and diffusion.