Effect of UV intensity on structure, water sorption, and transport properties of crosslinked N-vinyl-2-pyrrolidone/N,N′-methylenebisacrylamide films

UV photopolymerization was used to prepare films from N-vinyl-2-pyrrolidone (NVP) crosslinked with N,N′-methylenebisacrylamide (MBAA). These samples were crosslinked in the presence of water. Although the initial mixtures of water, NVP and MBAA were optically transparent, the final films were white, indicating that phase separation occurred during photopolymerization. The influence of UV intensity on the crosslinked NVP film structure was characterized using CryoSEM for cross-sectional imaging and Bio-AFM for imaging surface morphology. The influence of UV intensity on transport properties was characterized using dead-end filtration to measure water permeability and molecular weight cutoff (MWCO). Samples polymerized at high UV intensity had 2.7 times higher water permeability than those polymerized at low UV intensity, even though the structure, as probed via SEM and AFM, shows little to no significant changes. Higher UV intensity also led to somewhat higher MWCO values, indicating a tradeoff between water permeability and solute sieving characteristics.