Slow Solvation Dynamics near an Aqueous Micellar Surface

Abstract

Solvation dynamics of an ion near an aqueous micellar interface are studied in an atomistic molecular dynamics simulation of cesium pentadecafluorooctanoate (CsPFO) in water. The long time part of the polar solvation energy time correlation function $(C_s(t))$ of a tagged cesium ion at the micellar surface is found to decay very slowly-the long time decay at the surface is slower by 2-3 orders of magnitude compared to that in bulk water. Through an analysis of partial solvation time correlation functions, we find that the slow decay originates mostly from the interaction of the cesium ions with the polar headgroups; the slow orientational dynamics of water molecules on the surface seem to play only a secondary role. The probability distribution of the polar energy of ions show a non-Gaussian distribution with a tail toward the low-energy states.