Active control of electro-visco-fingering in Hele-Shaw cells using Maxwell stress

Viscous fingering is an extensively observed phenomenon in porous media or Hele-Shaw cells. In general, this instability is particularly difficult to control for given fluids and geometries. Therefore, investigating a control method of viscous fingering is quite attractive. Here, we present that electro-visco-fingering (EVF) in fluids with different relative permittivity shows a controllable performance under electric fields. The theoretical model is established from the perspective of force analysis to indicate that active control of EVF is achieved by the competition between the Maxwell stress jump and hydrostatic pressure gradient. In addition, an Electric Control number (E_C) is adopted to characterize the electric effect on EVF and experimentally confirmed for broad ranges of flow rates and voltages. Unlike the electro-osmotic flow, this method shows a considerable achievement in energy efficiency. Our work provides a new way to actively control viscous fingering and opens new routes for applications of interfacial instabilities.