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

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.