(596d) Brushing Off Salt Using a New Class of Synthetic Membranes

A new class of hydrophobic synthetic brush membranes are designed and tested.  Tethered polymer chains or brushes have attracted enormous interest recently for both engineering and biomedical applications such as to stabilize colloids, to reduce friction between surfaces, to design novel fluidic devices, and to fractionate proteins in chromatographic columns.  Here we tested them for desalination, which is an urgent challenge and an opportunity to meet future world water demand.  The membranes were prepared by graft-induced polymerization of hydrophobic vinyl monomers onto light sensitive poly(ether sulfone) nanofiltration support membranes, without initiating agents, using atmospheric pressure plasma.  Several hydrophobic vinyl monomers were tested to investigate the effect of chain length, the presence of linear versus branched chains, etc.  Membranes were characterized by using several techniques, such as ATR-FTIR, Atomic Force Microscopy (AFM) and Quartz Crystal Microbalance with Dissipation (QCM-D) monitoring to characterize the brush layer in terms of graft density, length and viscoelastic properties.  The modified membranes were finally tested in a high-pressure filtration unit against salt aqueous solution that reproduced seawater salinity.  The main novelty here is the use of hydrophobic brush-like structures as a selective skin or dense layer attached to a non-selective support membrane.  Possible advantages of these new desalination membranes include (i) ease and speed of synthesis as compared with interfacial polymerization and phase inversion, (ii) scalability, (iii) low cost production, and (iv) high fluxes due to hydrophobic resistance layer.  The optimization of these easy-to-synthesize and scale-up membranes could guarantee an alternative to traditional reverse osmosis membranes, which still remains the major method of choice for desalination of sea water.