Polymer-based membranes play a key role in several industrially important gas separation technologies, e.g., removing CO 2 from natural gas, with enormous economic and environmental impact. Here, we develop a novel hybrid membrane construct comprised entirely of nanoparticles grafted with polymers. These membranes are shown to have broadly tunable separation performance through variations in graft density and chain length. Computer simulations show that the optimal NP packing forces the grafted polymer layer to distort, yielding regions of measurably lower polymer density. Multiple experimental probes confirm that these materials have the predicted increase in "polymer free volume", which explains their improved separation performance. These polymer-grafted NP materials thus represent a new template for rationally designing membranes with desirable separation abilities coupled with improved aging characteristics in the glassy state and enhanced mechanical behavior.
The sorption of water in polylactide (PLA) was measured at various vapor activities (0−0.85) and temperatures using a number of experimental techniques, including quartz spring microbalance (QSM), quartz crystal microbalance (QCM), and in situ time-resolved Fourier transform infrared-attenuated total reflectance (FTIR-ATR) spectroscopy. Additionally, a prediction of the water sorption isotherm in PLA was obtained with the use of the nonequilibrium lattice fluid (NELF) model, where an excellent agreement between the model prediction and experimental sorption data was observed at different experimental temperatures (all below the glass transition temperature of PLA) for water vapor activities less than 0.65. Results from in situ time-resolved FTIR-ATR spectroscopy revealed that water is present predominately as dimers in PLA at water vapor activities less than 0.65, and the presence of larger hydrogen-bound water clusters was observed at water vapor activities >0.65. This provides a rationale for the deviation between the NELF model prediction and water sorption data at high vapor activities, where the NELF model does not account for the strong self-association interactions present in large hydrogen-bound water clusters. Furthermore, non-Fickian sorption kinetic behavior was observed with all the experimental techniques, and this highlights the nonequilibrium nature of the water−glassy polymer system and provides insight into the variability in the sorption isotherms reported in the literature.
The estimation of the solubility of fluid mixtures in polymeric phases is an essential prerequisite for membrane separations and in the design of several devices, such as chemical sensors: the presence of swelling and strongly interacting components in the fluid mixture can often cause rather large deviations from the pure component sorption behavior. For rubbery polymers, the usual equilibrium tools such as the multicomponent versions of the equation of state (EoS) models can be adopted, while for the case of glassy polymers, which are not at equilibrium, such an approach cannot be followed. The general model called nonequilibrium thermodynamics of glassy polymers (NET-GP) has proved to be a successful tool for predicting the solubility of pure gases, vapors and liquids in glassy polymers, and it is here applied to the prediction of multicomponent fluid solubility. In particular, three gas–gas–polymer systems, which show significant deviations from the ideal behavior, are examined at room temperature and various pressures: CH4/CO2 in poly(2,6-dimethyl-1,4-phenylene oxide) (PPO), C2H4/CO2, and N2O/CO2 in poly(methyl methacrylate) (PMMA). The maximum deviation between experimental data and the model predictions is equal to 10%, using as input only the pure component parameters and the binary parameters evaluated from pure gas sorption data. The model thus proves to be a reliable tool to estimate the mixed gas solubility in glassy polymers, in the common case in which such data are not experimentally available for the system of interest.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.