Electrokinetics meets electrohydrodynamics

Despite studying the same subject - electrically induced flow - the fields of electrokinetics (EK) and electrohydrodynamics (EHD) have developed separately, for different types of fluids and interfaces. In colloids or porous media, EK phenomena derive from the electro-osmotic slip of a liquid electrolyte across the neutral electric double layer on a solid surface. On the other hand, El-ID phenomena involve poorly conducting neutral fluids and solids, whose interfaces acquire net charge in response to electric fields. Over the past decade, combined theories of EK and El-ID have emerged for fluid/solid interfaces, and now Schnitzer & Yariv (J. Fluid Mech., vol. 773, 2015, pp. 1-33) have taken a major step towards unifying EK and El-ID for fluid/fluid interfaces. Following previous work by Baygents and Saville, they derive the classical Taylor-Melcher model of droplet El-ID as the large-field thin-double-layer limit of the electrokinetic equations, thus elucidating the ubiquitous 'leaky dielectric' approximation. Future work could consider the secondary electro-osmotic flow and electrophoretic motion of the drop (neglected here as small perturbations) and allow for more general EK models.