Professor at the University of Arkansas
Prof Wickramasinghe obtained his Bachelor’s and Master’s degrees from the University of Melbourne, Australia in Chemical Engineering. He obtained his PhD from the University of Minnesota, also in Chemical Engineering. He worked for 5 years in the biotechnology/biomedical industry in the Boston area before joining the faculty of Chemical Engineering at Colorado State University. He joined the Department of Chemical Engineering at the University of Arkansas in 2011 where he holds the Ross E Martin Chair in Emerging Technologies. Prof Wickramasinghe has published over 180 peer reviewed journal articles, several book chapters and patents and is co-editor of a book on responsive membrane and materials. He is active in the American Institute of Chemical Engineers and was the Meeting Program Chair of the 2013 Annual Meeting in San Francisco. He is a member of the Board of Directors of the North American Membrane Society. He is the current director of the Membrane Science, Engineering and Technology (MAST) Center at the University of Arkansas, a NSF Industry/University Cooperative Research Center.
Prof Wickramasinghe’s research interests are in membrane science and technology. His research focuses on synthetic membrane-based separation processes for purification of pharmaceuticals and biopharmaceuticals, treatment and reuse of water and for the production of biofuels. Typical unit operations include: microfiltration, ultrafiltration, virus filtration, nanofiltration, membrane extraction etc. A current research focus is surface modification of membranes in order to impart unique surface properties. His group is actively developing responsive membranes. These membranes change their physical properties in response to changed environmental conditions. A second research focus is the development of catalytic membranes for biomass hydrolysis by grafting catalytic groups to the membrane surface.
Modification of membrane surfaces by grafting polymer brushes from the surface has been shown to impart unique surface properties. Here we focus on magnetically responsive membranes where magnetically responsive polymer chains are grown from the membrane surface. We have developed a range of microfiltration1, ultrafiltration2 and nanofiltration3 membranes by grafting magnetically responsive polymer brushes from the membrane surface. Atom transfer radical polymerization (ATRP) has been used to graft poly-hydroxyethyl methacrylate (polyHEMA) from the surface of the membrane. Superparamagnetic nanoparticles have been attached to the chain ends. In an oscillating magnetic field, movement of the magnetically responsive nanobrushes leads to suppression of concentration polarization resulting in higher permeate fluxes and better rejection. We have also grafted poly(N-isopropylacrylamide) a thermo-responsive polymer that exhibits a lower critical solution temperature, using ATRP, from the surface of the membrane4. By carefully choosing the frequency of the oscillating magnetic field, movement of the polymer chains can induce mixing. Using much higher frequencies, around 1,000 Hz, heating will lead to collapse of poly(N-isopropylacrylamide) layer as the temperature of the grafted polymer layer increase above the lower critical solution temperature of the grafted poly(N-isopropylacrylamide).
Unlike nanofiltration and microfiltration membranes where the majority the polymer chains are grafted from the barrier layer or the inside pore surface respectively, in the case of ultrafiltration membranes significant grafting can occur from both the barrier layer and the internal pore surface. In addition, given the smaller pore sizes compared to microfiltration membranes, pore plugging by the grafted polymer chains must be avoided. We have developed a novel technique to selectively graft from the external barrier layer and not the internal membrane pore surface. We show that the magnetically responsive polymer brushes can have a significantly different effect on rejection and flux of model feed streams consisting of proteins such as bovine serum albumin, depending on their location on the membrane barrier layer or in the pores. Our work highlights the importance of being able to control not only the three-dimensional structure of the grafted polymers but also their location; from the membrane barrier layer or from the inside pore surface.
References 1. H. H. Himstedt, Q. Yang, X. Qian, S. R. Wickramasinghe, M. Ulbricht (2012), Toward remote-controlled valve functions via magnetically responsive capillary pore membranes’, J Membr. Sci., 423, 257-266. 2. B. M. Carter, A. Sengupta, X. Qian, M. Ulbricht, S. R. Wickramasinghe (2018), Controlling external versus internal pore modification of ultrafiltration membranes using surface-initiated AGET-ATRP, J Membr. Sci, 554, 109-116. 3. Q. Yang, Q., H. H. Himstedt, M. Ulbricht, X. Qian, X., S. R. Wickramasinghe, Designing magnetic field responsive nanofiltration membranes, J Membr. Sc., 430 (2013) 70-78. 4. X. Qian, Yang, Q., Vu, A. T., Wickramasinghe, S. R. (2016), ‘Localized Heat generation from Magnetically Responsive Membranes’, Industrial & Engineering Research, 55 (33), 9015-9027.