ELECTROHYDRODYNAMIC LUBRICATION WITH THIN DOUBLE-LAYERS

Sliding of one charged body past another in an electrolyte solution induces a streaming potential in the fluid between the surfaces which in turn generates an electrokinetic force on the bodies. In this paper, we extend our previous lubrication analysis for bodies bearing thin double layers from two-dimensional to three-dimensional flows and to squeezing as well as sliding motion. A general differential equation for the streaming potential is derived which is analogous to Reynolds' equation for pressure. When the double layer is thin compared to the minimum distance separating the two bodies, this electrokientic force tends to be small compared to viscous forces. However, for sliding motion, one component of the electrokinetic force acts to push the bodies apart; this component has no viscous counterpart. This "electrokinetic lift" is always repulsive, regardless of the relative signs or magnitudes of the ζ potentials and can be comparable to double-layer repulsion for fluids of low conductivity. Electrokinetic lift may reduce the elution volume of particles in chromatographic columns, inhibit the capture of particles from moving fluids, or cause detachment by shear of particles from solid surfaces. © 1990.