CDS&E: Organization and Dynamics of Charged Molecules in Heterogeneous Media

Nanofluidics systems like nanochannels, which have one dimension comparable to or even smaller than the Debye length, possess an electrostatic potential that can be significantly modulated by soft ionic structure inside and on the other side, external field and dielectric heterogeneity will affect the transport properties dramatically. The nanometer scale of the structure allows the discovery of a new range of phenomena that has not been possible in traditional microfluidics. Present studies on nanofluidics mainly deal with a simple symmetric monovalent electrolytes because it is a simple physical system that can be easily understood by Poisson Boltzmann theory. However, real applications may involve multivalent ion species as well as the dielectric interfaces. It is crucial, therefore, that we understand how fluid and ions flow through nanochannels and in what way their transport differs from expectations based on classical hydrodynamics and the Poisson-Boltzmann equation. The effect of correlations, finite size of molecules, hydrogen bonding and other short range interactions are all expected to play a role in understanding of fluid flow and ion transport. Previous MD simulations carried out did not use any adjustable parameters, including ion correlations, finite size of molecules and dielectric heterogeneity, and should in principle yield numerically exact results for the primitive model. We note that these simulations, which, based on a true energy functional, are versatile enough to treat the case of multiple and curved interfaces, multivalent salts, asymmetric ion sizes to study the dynamical evolution of the soft ionic structure. Using our molecular dynamics method we propose to study how ionic transport properties of electrolytes under dielectric confinement are influenced by different electrolyte concentrations, multivalency, and dielectric heterogeneity. This will provide valuable information for manipulating and designing relevant nanofluidic devices.