(142co) Electrohydrodynamic Drop Deformation: Inertial Overshoot and Long-Time Tail

The motion of a charged micron-sized particle instigated by a hydrodynamic flow or electric field is of fundamental interest in colloid science. Notably, the majority of previous work in this area has been restricted to the “linear-response” regime wherein the ionic (Debye) cloud that screens a charged particle in an electrolyte solution is only slightly distorted by the "weak" applied flow or field. In this poster, we instead focus on "strong" flows or electric fields, wherein the Debye cloud can be highly distorted.  Specifically, we consider two paradigmatic problems, via numerical solution of the nonlinear electrokinetic equations: (i) a charged particle held fixed in a uniform fluid flow (the strong flow regime being relevant to ultra-centifugation and streaming flows in microfluidics); and (ii) the electrophoretic motion of a sphere in an imposed electric field (the strong field regime being relevant to electrophoresis in non-polar solvents). In case (i) we determine the force-velocity relationship for a wide range of imposed flow strengths and Debye layer thicknesses. In case (ii) we compute the electrophoretic mobility as a function of the applied field strength. In both cases, we observe marked departures from the respective classic linear-reponse predictions, primarily as a result of the strongly deformed Debye layer in the high flow/field regime.