S-shaped velocity deformation induced by ionic hydration in aqueous salt solution flow

Abstract

Ionic hydration shells are the most noticeable microscopic feature in an aqueous salt solution, and have attracted attention due to their possible contribution to its flow behavior. In this paper, we find by molecular dynamic simulations that an S-shaped velocity profile is induced by the ionic hydration shells in the nano channel flow. Our theoretical analysis implies a linear relationship between the energy density inside the first hydration shell of the ions and the deformation strength of the velocity profiles of aqueous salt solutions, where the deformation strength is quantified by the curvature length defined by the linear deviation extended from the velocity profile. Our simulation results confirm that such a linear relationship holds for chloride salt solutions with monatomic cations, e.g., K, Na, Ca, Mg, Al and the Na/Ca models by varying the valence number of Na and Ca in the salt solutions. Furthermore, the influence of the flow velocity and the channel width upon the velocity deformation strength are also investigated. Our results indicate that the calculated curvature length provides a numerical evaluation for nano flow behavior and would be helpful in nanofluidic device design.