(731d) Molecular Dynamics Simulations of Polyamide Water Purification Membranes

Nanofiltration and reverse osmosis membranes are widely used for water treatment and purification. Here we explore the molecular level properties of the membrane nanostructure and charge as well as nanoscale transport of water and contaminants using molecular dynamics simulations. Both meta-phenylenediamine (MPD) based polyamide membranes (typical of reverse osmosis membranes) and piperazine based polyamide membranes (typical of nanofiltration membranes) are constructed using a virtual polymerization technique. In both cases, accounting for charged carboxylate end groups is a challenging computational issue. The distribution of open volume within the molecular structure and the polymer density are compared between the MPD and piperazine membranes. Non-equilibrium simulations are performed in which water, modeled using the TIP3P model, is forced at high pressure through both types of membranes. We also consider uncharged organic solutes to assess the transport of neutral species. Finally, we consider ion complexation with the charged carboxylate end groups to examine the impact of solute-membrane charge interaction. This approach of non-equilibrium molecular dynamics simulations to examine water and solute transport in polyamide membranes at the molecular level holds great promise for designing the next generation of membranes for desalination and other applications. Funded by the Northwestern University Center for Water Research.