(441b) Molecular Simulation of Macromolecular Transport through Nanoporous Membranes

To design efficient nanoporous membranes a critical need exists to establish how pore size and pore chemistry affect the interfacial transport of macromolecules across membranes. A novel hybrid Monte Carlo and molecular dynamics simulation technique was implemented to elucidate the equilibrium behavior and transport properties of a model macromolecule as it navigated across a nanoporous polymer thin film (i.e., a nanofiltration membrane). A two-dimensional system, where a nano-pore separates two reservoirs on each side filled with water-like solvent particles was simulated. A steady-state flux of the solvent was established by imposing different chemical potentials within both reservoirs. The density and velocity profiles, viscosity, and flux of the solvent particles was measured in the nanopore system as a function of pore size. A non-constant density profile across the pore was found for small pore sizes, which results in a slip flow velocity profile. A linear polymer chain was added into the top reservoir to study structural rearrangements of the chain as it moved into the nano-confined spaces. The chosen model linear homopolymer was one that had interactions representative of poly(ethylene oxide) (PEO) when a PEO chain is dissolved in an aqueous environment. The structural rearrangements of the PEO chain as it passes through the nanopore under an imposed chemical potential gradient was quantified by measuring spatial configurations (i.e. end-to-end distance, radius of gyration, etc.) of the polymer as a function of solvent quality, polymer chain length, nanopore diameter, and PEO-nanopore wall interactions. These computational studies provide a more detailed picture of the underlying physical mechanisms that drive macromolecular transport through nanopores, and, in particular, how dimensionally-large macromolecules (i.e., with large radii of gyration) enter and move through dimensionally-small pores (i.e., small radii nanopores). The insights gained from these studies will aid in the development of more cost-effective water purification systems in separation technologies for a range of industrial applications.