Multicomponent transport of methanol and sodium acetate in poly(ethylene glycol) diacrylate membranes of varied fractional free volume

Abstract

Polymer membranes are critically important to the advancement of next generation technologies in energy devices, water purification, and industrial separations. Understanding relationships between membrane structure, physical properties, and transport phenomena is critical to developing next-generation membranes for applications that require the selective transport of neutral and ionic molecules. Fractional free volume (FFV) is one critical membrane characteristic in dense polymer membranes as it forms the pathways for molecular transport. Here, we investigate the impact of varied FFV on the transport of methanol, sodium acetate, and their mixture in a series of polyethylene glycol diacrylate (PEGDA, n = 13) membranes prepared with a range of FFV. Membranes are fabricated by UV-photopolymerization where FFV is varied through control of the water content in pre-polymerization solutions. Water uptake of fabricated membranes is characterized as a proxy for the varying FFV. Solute permeabilities are measured in custom-built diffusion cells for methanol, sodium acetate and their mixture with downstream receiver cell solute concentrations measured via in situ attenuated total reflectance Fourier transform infrared (ATR FTIR) spectroscopy. Membrane permeability varied by up to a factor of 6 as the prepolymerization water content, and thereby FFV, of the membranes was varied. Furthermore, distinct, and increasing, differences in the magnitude of extracted permeabilities between single solute and combined solute experiments are observed as the FFV increases and these differences are attributed to a combination of assisted and competitive transport.