Experiments on rotating charged liquid drops

Abstract
Shapes and stabilities of freely rotating charged drops are investigated experimentally. Liquid drops approximately 3 mm in diameters were suspended in air by an electrostatic levitator and rotated by a torque which was acoustically generated in the levitation chamber. As the drop angular velocity was increased from the static state, families of axisymmetric, triaxial, dumbbell shapes, and eventual fissioning have been observed. With the assumption of ‘‘effective surface tension’’ by which the surface charge simply modified the surface tension of neutral liquid, the results from drops carrying low level surface charges agree quantitatively well with the Brown and Scriven’s prediction. The normalized angular velocity at the bifurcation point agrees with the predicted value of 0.56 to within 3%. However, as the sample charges approached the Rayleigh limit, the results indicated a marked deviation from those of low charges. Drops of high charges showed asymmetric dumbbell shapes and the drop break‐up directly from the axisymmetric shapes. Also discussed in this paper are methods of measuring drop charges and surface tension of highly viscous liquids in microgravity laboratories.