Polyamide-POSS hybrid membranes for seawater desalination: Effect of POSS inclusion on membrane properties

We have shown using both experiments and simulations that incorporation of polyoctahedral oligomeric silsequioxanes (POSS) into the active layer of polyamide (PA) thin film composite membrane results in higher water flux and salt rejection than pure PA membranes. We report that the water flux increased by a factor of 1.32 and salt rejection increased from 99.0% to 99.62% for the PA-POSS. Molecular dynamics simulation was employed to study the effect of POSS on membrane polymerization, water and salt diffusion and free volume. Quantities, such as water diffusivity, water partition coefficient, fractional free volume and range of free volume size computed on the equilibrated configurations, increased on the inclusion of POSS in PA membranes. Moreover salt diffusivity was lower in PA-POSS than PA. Therefore from the simulation study, it was concluded that the introduction of POSS into PA membrane improved (a) porosity of composite membrane, (b) hydrophilicity and (c) charge on the membrane. These effects explain the increase of water flux and salt rejection in nanocomposite membranes.