Electrohydrodynamic deformation and bursts of liquid drops

Abstract

In 60 Hz electric fields, liquid drops suspended in a second immiscible liquid deformed into prolate spheroids oriented in the direction of the field in 22 drop/medium combinations studied experimentally. In steady fields, oblate or prolate spheroids were formed depending upon the dielectric constants and resistivities of the drop and medium. In systems yielding oblate spheroids, a critical frequency existed at which the drop remained spherical at all field strengths. Electrohydrodynamic streaming near the surface of the drop occurred as predicted by Taylor. A theory, valid for both steady and alternating fields, was developed which predicts the conditions leading to oblate and prolate spheroids and which reduces to Taylor’s equations for conducting dielectrics in steady fields and to the equations for perfect dielectrics in steady and alternating fields. The theory explains the general types of deformation and electrohydrodynamic flow which were observed and predicts several interesting new modes of behaviour. In most cases the measured deformations were greater than calculated from the theory; various explanations for this discrepancy are advanced, but no definite conclusions are reached. At high field strengths the drops burst in two basically different ways which we have designated as electric and electrohydrodynamic burst, the first caused by electric stresses alone and the second by a combination of electric and hydrodynamic stresses.