Reis, Rackel (2016) Surface modification of thin-film composite membranes by direct energy techniques. PhD thesis, Victoria University.

Abstract

Reverse osmosis (RO) for water desalination is a pressure driven technology that utilizes thin-film composite (TFC) membranes as its core technological component. The selectivity of commercial RO TFC membranes is provided by a ~100 nm thin semidense and negatively charged poly(amide) (PA) layer, where performance is highly influenced by electrostatic interactions between the liquid (water and solutes) and the net surface charge of the membrane surface. Furthermore, the interfacial polymerization manufacturing process leads to the formation of a rough surface, due to surface tensions effects between the two non-miscible phases - carboxylate and aromatic amide. Over the past four decades, the remarkable development of such membrane materials has contributed to reducing RO energy consumption and increasing salt rejection to the 99.9% level. However, the chemistry and morphology of the PA layer continues to promote unfavorable affinity with contaminants in the water – a phenomenon referred to as fouling. ‘Foulants’, such as biological, inorganic and organic compounds, may aggregate and accumulate on surface due to chemical affinity, electrostatic interactions and physical adsorption in between the protusions of the rough material. Such interactions across the surface of the membranes lead to reduced water transport and in severe cases may cause membrane failure. Therefore, new routes to further refine the properties of PA membranes are still required to develop more permeable membranes with controlled surface charge.

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