Electrolubrication in liquid mixtures between two parallel plates

Abstract

We describe theoretically ``electrolubrication'' in liquid mixtures, the phenomenon where an electric field applied transverse to the confining surfaces leads to concentration gradients that alter the flow profile significantly. When the more polar liquid is the less viscous one, the stress in the liquid falls on two electric-field-induced thin lubrication layers. The thickness of the lubrication layer depends on the Debye length and the mixture correlation length. For the simple case of two parallel and infinite plates, we calculate explicitly the liquid velocity profile and integrated flux. The maximum liquid velocity and flux can be increased by a factor $\alpha$, of order $10$--$100$ or even more. For a binary mixture of water and a cosolvent, with viscosities $\eta_w$ and $\eta_{\rm cs}$, respectively, $\alpha$ increases monotonically with inter-plate potential $V$ and average ion content, and is large if the ratio $\eta_{\rm cs}/\eta_w$ is large.