In this work, the water order and dynamics in hydrated films of flat asymmetric cellulose acetate (CA)/silica, CA/SiO2, and hybrid membranes, covering a wide range of nanofiltration (NF) and ultrafiltration (UF) permeation properties, were characterised by deuterium nuclear magnetic resonance (DNMR) relaxation. The range of NF/UF characteristics was attained by subjecting three CA/SiO2 membranes, prepared from casting solutions with different acetone/formamide ratios to drying post-treatments of solvent exchange and conditioning with surfactant mixtures. Post-treated and pristine CA/SiO2 membranes were characterised in terms of hydraulic permeability, selective permeation properties and molecular weight cut-off. These results were correlated with the DNMR relaxation findings. It was found that the post-treatment by solvent exchange caused membrane shrinkage that led to very different permeation characteristics and a significant enhancement of the DNMR relaxation observables. In contrast, conditioning with surfactant solutions exhibited a weaker effect over those properties. Scanning electron microscopy (SEM) images were obtained for the membranes post-treated with solvent exchange to confirm their asymmetric nature. This work provides an essential indication that DNMR relaxometry is a reliable tool to characterise the asymmetric porous structures of the NF/UF CA/SiO2 hybrid membranes.
Keywords: asymmetric CA/SiO2 membranes; deuterium relaxometry; phase inversion and sol-gel; ultrafiltration/nanofiltration; water dynamics in confined media.