Transport behavior of pressure-driven electrolyte solution through a surface-charged nanochannel

The transport behavior of a pressure-driven electrolyte solution through a surface-charged nanochannel is investigated using molecular dynamics (MD) simulations. Similar to pure water, the relationship between the applied pressure (P) and the average transport velocity ($\overline{v}$) of the electrolyte solution is roughly linear, which matches with the theoretical solution very well. The friction coefficient λ is used to describe the transport behavior (a higher λ leads to a lower $\overline{v}$), which scales with the slope of the P- $\overline{v}$ relationship and increases with the increases of both the charge density of the channel wall σ and the electrolyte concentration n. The physical mechanism is found as follows: the solid–liquid interaction energy between the channel wall and the liquid inside the channel decreases with both σ and n (being more negative), which makes it more difficult for the liquid boundary layer to slide against the channel wall, leading to a higher λ. In addition, the increase of σ also causes a significant decrease of the liquid–liquid interaction energy but the opposite effect is found with the increase of n. However, λ increases with the increase of both σ and n, suggesting that the relationship between λ and the liquid–liquid interaction energy is more complicated for an electrolyte solution, different from the corresponding result of pure water. (paper)