Electrosprayed Polymerization: A Green, Additive Approach for Making Highly Tunable Polyamide Films for Desalination

In membrane based desalination processes, the thin film composite (TFC) membrane is an industry standard which uses interfacial polymerization technique to form an ultra-thin polyamide layer on the surface of polymeric substrates. Remarkably, in 30 years of using this approach, the RO industry has yet to create a polyamide film onto a supporting membrane with controllable thickness, roughness and properties that are independent from the substrate properties. While the film formation essentially is “self-controlled”, the reaction itself is simply allowed to proceed uncontrolled. Thickness and roughness impact membrane permeance and fouling propensity, respectively, and controlling these parameters could greatly benefit any process that uses a TFC membrane. We developed a highly scalable, and green method for making tunable polyamide films for desalination. The method uses electrospraying technique to spray-deposit monomer solutions directly on to substrate which react to form the polyamide film. This is achieved through the use of lypophilic ionic liquid in the organic phase that contains one of the monomers. Comparable desalination performance to that of commercial membranes with sub-2 nm smoothness and a sub-4 nm resolution in film growth was achieved regardless of substrate properties. We also demonstrated the formation of a bulky 1 µm thick polyamide film of similar chemical structure for the first time. We further verified a two orders of magnitude lower chemical footprint using electrosprayed polymerization than the conventional method.