(756f) Chemically Dependent Transport of Small Polar Solutes in a Cross-Linked Hii Phase Lyotropic Liquid Crystal Membrane

Authors: 
Coscia, B. J. - Presenter, University of Colorado Boulder
Shirts, M. R., University of Colorado Boulder
The pores that constitute cross-linked lyotropic liquid crystal (LLC) membranes are chemically complex and uniform in size which makes them promising for selective separations. We have developed an atomistic molecular model of an LLC membrane that is maximally consistent with experimental X-ray diffraction for the purpose of studying small molecule transport within it.

We have characterized transport of water, sodium ions and 20 small polar solutes within the pores of our model. We found that the transport rate of a species is dependent not only on molecular size, but on chemical functionality as well, leading to anomalous diffusive behavior. Electrostatic interactions between the membrane and solutes provide an interesting diversity of mechanistic behaviors. In general, all solutes perform intermittent hops between lengthy periods of entrapment. Three different trapping mechanisms are responsible for this behavior. First, solutes that drift out of the pore can become entangled among the dense monomer tails. Second, solutes can donate hydrogen bonds to the monomer head groups. Third, solutes can coordinate with sodium counter ions. The degree to which a solute is affected by each mechanism is dependent on the chemical functionality of the solute.

We have used our detailed mechanistic understanding in order to construct a stochastic model which we can use to project the long term behavior of the solutes and ultimately predict selectivity. Using the insights developed in this study, we can begin to think about how to redesign existing LLC membranes in order to perform solute-specific separations.