Influence of residual conductivity on the stability threshold of a dielectric liquid surface under electric field and charge injection

Two different Electrohydrodynamic (EHD) instabilities are found to coexist in experiments where an electric field, together with injection of charge, is applied perpendicularly onto an interface between air and a very low-conducting liquid. One is the classical EHD instability, while the other is the so-called Rose-window instability. A preliminary theoretical analysis is made of the effect upon the interface instability of a certain residual ohmic conductivity in the liquid. The rise of charge density in the liquid near the interface is enhanced by the presence of the residual conductivity, which could favour the generation of low wave-number instabilities.