Northwestern University Robert R. McCormick School of Engineering and Applied Science

Richard M. Lueptow's Research Group

Reverse Osmosis

Molecular dynamics simulations can be used to study water and contaminant transport in reverse osmosis membranes at the atomic level. This video shows reverse osmosis filtration of 2-propanol contaminant molecules in water over 16.2 ns. The polymer structure is a polyamide membrane that is about 4 nm thick (about 50 times thinner than actual reverse osmosis membranes). Water molecules, which are not shown, buffet the green propanol molecules and the membrane (Brownian motion). Most propanol molecules remain on the left side of the membrane even though a very high pressure is applied on this side to force water through the membrane. Some propanol molecules slip through the membrane to the right side, where the pressure is lower. One propanol molecule is labeled red to make it easy to follow. Note how this molecule displays Brownian motion and hops from pore to pore as it transits the membrane. This simulation was done by Dr. Meng Shen under the direction of Professors Sinan Keten and Richard M. Lueptow at Northwestern University, 2015.