(709g) In situ Monitoring of Emergent Transport in Polymer Membranes

Authors: 
Beckingham, B. S., Auburn University
Miller, D. J., Lawrence Berkeley National Laboratory
Dobyns, B., University of South Alabama
The permeation of aqueous solutes through membranes is of critical importance in many applications, from traditional membrane separations to fuel cells. Transport of small-molecule solutes through polymeric membranes is typically characterized in single-component permeation experiments. Traditionally the techniques used to measure organic permeation through a membrane, e.g. gas chromatography, require aliquot sampling and are limited by their ability to resolve the analytes of interest and water. Here, we utilize in-situ ATR FTIR spectroscopy to examine emergent transport phenomena, where the transport of a small molecule is affected by the presence of another solute, in real time without aliquot sampling. First, we quantitatively determine the concentration of single and multicomponent mixtures of various solutes including methanol, formate and acetone. So validated, we apply this methodology to monitoring the permeation of single and multicomponent mixtures across commercially available membranes, such as Nafion 117, in situ using a diffusion cell. Membrane permeabilities are extracted from time-resolved half-cell concentration data using free volume models. We demonstrate the capability of this methodology to simultaneously measure permeation of multiple components, provided that each analyte has a distinct IR signature. Membrane permeabilities and selectivities obtained from the single component permeation experiments are compared to those calculated for solutes in multicomponent permeation experiments. In some instances, the membrane permeability to an organic solute substantially deviates, sometimes by orders of magnitude, when co-solutes are present. Similarly, membrane selectivities calculated from multicomponent diffusion experiments differ significantly from those calculated from single component permeabilities.