The transport properties of reverse osmosis (RO) polyamide(PA) membranes are largely determined by their chemistries and fabrication conditions. Detailed understanding of the structure-performance relationships in RO membranes is critical to the development of membrane technology with improved flux and/or rejection. The relationship between molecular structure and polymer dynamics is a pervasive question in polymer science, dating back to the early mean field reptation models of deGennes and continues today in more complex multi-scale simulations which involve chain cooperativity. Water motion, in particular, is critical to the function of biopolymers, separation membranes (e.g., for water purification or the production of biofuels). Observed dynamic coupling between the water motions and the polymer dynamics in concentrated aqueous polymer systems indicates that the mobility of the polymer matrix is critical to facilitate the water mobility in hydrated polymer systems. Membranes typically involved cross-linked polymers that are ill-defined; yet, these features have important implications for the polymer dynamics and water transport. Thus, there is a need to understand the effect of the structural architecture on the dynamics in a controlled manner. PA membranes with varying carbonyl content were fabricated. Physiochemical properties of the membranes, i.e. thickness, morphology, molecular bonding, and chemical composition, were characterized by atomic force microscopy (AFM), low-voltage and variable-pressure field-emission scanning electron microscopy (FESEM), energy-dispersive x-ray spectrometry (EDXS), cryo-scanning/ transmission electron microscopy (S/TEM), electron-energy-loss spectroscopy (EELS), and solid state NMR (SSNMR). The dynamics of both water and the polymer was measured using quasi-elastic neutron scattering (QENS). The mobility of salt within the membrane was measured using electrochemical impendence spectroscopy (EIS). Finally, the water and salt dynamics as they relate to the carbonyl content of the membrane were correlated with membrane performance.

Investigating the effect of carbonyl content on water and salt dynamics in interfacially polymerized polyamide membranes

2019 Fall National Meeting

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