Molecular dynamics simulation of electrolyte solution flow in nanochannels and Monte Carlo simulation of low density methyl chloride monolayer on graphite

Electroosmotic flow is studied by non-equilibrium molecular-dynamics simulations in a model system chosen to facilitate comparison with existing continuum theories. The model system consists of spherical ions and solvent, with stationary, uniformly charged walls that make a channel with a height of 20 particle diameters. We find that hydrodynamic theory adequately describes simple pressure-driven flow (Poiseuille flow) in this model. However, when combined with Poisson-Boltzmann theory to describe electroosmotic flow, the continuum theory fails in important situations. The failure is traced to the exclusion of ions near the channel walls resulting from reduced solvation of the ions in that region. When Poisson-Boltzmann theory is adjusted to account for the exclusion of ions near the walls, agreement with hydrodynamic theory is restored.; Monte Carlo simulation using an all-atom potential model is applied to evaluate two crystal structures of low density methyl chloride monolayer that have been proposed based on diffraction experiments. The equilibrium configuration proposed by Morishige, Tajima, Kittaka, Clarke and Thomas was found to be lower in energy than an alternative structure proposed by Shirazi and Knorr. The first-order melting transition of the monolayer crystal was found to occur between 85K and 90K, in qualitative agreement with experiments. However, the melting point from simulations is lower than the experimental melting point of 120K. After melting, short-range order within the methyl chloride fluid phase was found.