(84d) Understanding Transport of Small Solutes in the Pores of a Nanostructured Lyotropic Liquid Crystal Membrane

Lyotropic liquid crystals (LLCs) are amphiphilic molecules that have the ability to form ordered nanostructures. When combined with ~10 wt % water, the liquid crystalline monomer, NA-GA3C11, forms the inverted hexagonal (HII) phase which is characterized by uniform-sized, sub-nm, straight hydrophilic pores. This geometry is ideal for transport in aqueous membrane separation processes. With a complete understanding of the mechanisms that govern transport of small solutes within these nanopores, we can modify LLC monomers in order to tune the size and chemical environment of the pores for solute-specific separations.

We have used molecular dynamics simulations in order to form a detailed atomistic model of this system by maximizing its consistency with experimental observables such as 2D wide angle X-ray scattering patterns and ionic conductivity measurements. Using our atomistically detailed model, we study the transport mechanisms of a range of neutral solutes within the pores. We calculate the diffusion constant along the pore for each solute, and examine transport mechanisms as the rates of diffusion change. We also calculate the potential of mean force (PMF) using umbrella sampling in order to construct free energy profiles along the pore. We use this information to understand selectivity based on both size and chemical details of the solute. With this understanding, we can identify bottlenecks in membrane design so that we can suggest new LLC monomer structures to be tested experimentally.