Chain and Solvent Dynamics in Polymer Membrane Films Supported on a Polymeric Substrate

Polymeric membranes used for separation applications typically consist of thin films of cross-linked gels supported on a substrate that is often polymeric. The separation efficiency of such membranes is governed by the dynamics of the membrane polymer and solvent molecules, which in turn is affected by the polymer-solvent and polymer-substrate interactions. In this work, we have used atomistic molecular dynamics (MD) simulations to determine the effects of a polysulfone (PSF) support on the volumetric properties and chain dynamics in thin films of a model membrane material, namely, polyacrylate. The effects of the support polymer on the dynamics of water and ethanol molecules in these polyacrylate networks are also investigated. Three polyacrylate networks that are composed of homopolymers and a 50-50 random copolymer of n-butyl acrylate and 2-hydroxyethyl acrylate were studied. The results show that the volumetric and dynamic properties of bulk regions of the polyacrylate layer show a very similar behavior to that of their respective unsupported systems. However, at the interface, the dynamics of each layer is affected by the other. The interfacial dynamics of polyacrylate networks is suppressed compared to their bulk regions, while the dynamics of PSF at the interface is enhanced compared to that of its bulk region. The dynamics of water and ethanol molecules in the bulk and interfacial regions of the polyacrylate layers follows the same trend as the dynamics of the polyacrylate networks in the corresponding regions. Our results indicate that polymeric supports affect chain dynamics in the interfacial regions of the supported films; these changes, in turn, affect the penetrant transport through the films, thus having direct implications on the separation characteristics of the supported polymeric membrane systems.