School of Mechanical Engineering Seminar
Monday, March 25, 2019 at 14:00
Wolfson Building of Mechanical Engineering, Room 206

Molecular-level transport mechanisms in desalination membranes via molecular dynamics simulations

Richard M. Lueptow

Department of Mechanical Engineering, Northwestern University, Evanston, IL, USA

Molecular-level water permeability and solute rejection can be studied for polymeric reverse osmosis (RO) and nanofiltration (NF) membranes using non-equilibrium molecular dynamics simulations. Such simulations are computationally challenging but can provide Ångström-level information not otherwise available. For example, solute molecules display Brownian motion within a nanoscale pore for 1-5 ns before hopping quickly to another nanoscale pore as they pass through the membrane. Furthermore, the solute rejection depends on both the size of a solute molecule and the chemical interaction of the solute molecule with water molecules and the molecular chains of the polyamide membrane. When solute molecules have to shed at least one water molecule from their solvation shell to pass through the membrane molecular structure, the water-solute pair interaction energy governs solute rejection.  Thus, small organic solutes that more easily shed water molecules pass through

the membrane readily compared to ions.  Hydrogen bonding with the membrane polymer chains results in high rejection for solute molecules like urea.  These findings underline the importance of the solute’s solvation shell and solute-water-membrane chemistry in solute transport and rejection in RO membranes.  Moreover, the approach of non-equilibrium molecular dynamics simulations to understand and predict flux and rejection mechanisms in polymeric membranes at the molecular level holds great promise for designing the next generation of membranes for desalination and other applications.

Funded by the Institute for Sustainability and Energy at Northwestern (ISEN) with computing resources from XSEDE, which is supported by NSF grant ACI-1053575.

Bio:

Richard M. Lueptow is Senior Associate Dean at the McCormick School of Engineering and Applied Science, Co-Founder of the Master of Product Design and Development Program, Professor of Mechanical Engineering, and Charles Deering McCormick Professor of Teaching Excellence at Northwestern University.  He received his BS in engineering (1978) from Michigan Technological University and his master’s degree (1980) and doctorate (1986) in mechanical engineering from the Massachusetts Institute of Technology.  He has five years of product development experience in the biomedical industry and three decades of academic experience on the faculty at Northwestern University.  His research interests and expertise range from fundamental flow physics to water purification on manned spacecraft to planetary acoustics. His current research focuses on filtration processes, nonlinear systems, and granular dynamics.  He has published over 150 journal papers and 6 patents, received numerous teaching and research awards, and is a Fellow of both the American Physical Society and the American Society of Mechanical Engineers.