(343i) Active Control of Viscous Fingering Using Electric Field

Viscous fingering is a widely observed phenomenon, in which finger-like instabilities occur at the interface of two fluids, whenever a less viscous phase displaces a more viscous phase.This instability is notoriously difficult to control, especially once the viscosity ratio and geometry are specified. Here we demonstrate experimentally for the first time the active control of viscous fingering of two given liquids for given geometry and flow rate in a Hele-Shaw cell, by taking advantage of electro-osmotic flows along the surfaces confining the fluid via applying an external electric field. Depending on the direction of electric field, the induced secondary electro-osmotic flows either assist or oppose the hydraulic flow, effectively reducing or increasing the flow resistance, leading to the control of interface stability. The concept, ”electrokinetic thinning/thickening”, is proposed to explain the macroscopic observations of the experiment. Theoretical predictions of linear stability are confirmed experimentally for a broad range of immiscible electrolyte displacements. Potential applications include enhanced oil recovery, tunable adhesion, drug delivery, patterning of soft materials and enhancing mixing in microfluidic devices.