(247f) Gibbs Ensemble Monte Carlo Simulations for Additive Loading in Surfactant Bilayers

Authors: 
Minkara, M., University of Minnesota
Venteicher, C., University of Minnesota
Siepmann, J. I., University of Minnesota
Understanding solute uptake into soft micro-structured materials, such as bilayers and micelles, is of specific interest in the pharmaceutical, agricultural, and personal care industries. Currently, there are continuum-solvation methods available that can rapidly estimate the amount of a solute that will load into these soft micro-structured materials. However, these methods do not give any insight into the structural orientation and positioning of the solutes at a molecular level. To obtain this insight, we utilize the Shinoda-Devane-Klein (SDK) force fieldin conjunction with configurational-bias Monte Carlo simulations in the osmotic Gibbs ensemble. One simulation box contains a lamellar system comprised of a bilayer formed by triethylene glycol mono-n-decyl ether (C10E3) surfactants surrounded by water with a 50/50 surfactant/water weight ratio. This simulation cell is allowed to undergo volume and shape fluctuation, by changing either the z cell length independently or the x and y cell lengths in a coupled fashion and is found to have a stable lamellar phase in agreement with experiment.The other simulation box is a vapor-phase reservoir containing solute molecules at a constant applied pressure, and only solute molecules are allowed to transfer between the two simulation boxes. We study both the adsorption isotherm and structural effects of n-nonane, 1-hexanol, and ethyl butyrate on the bilayer at several different reduced pressures with respect to the saturated vapor pressure of the solutes. Additionally, we study the binary adsorption of n-nonane and 1-hexanol and observe a possible synergistic enhancement of their uptake.