Electrorotation of Deformable Fluid Droplets

Abstract

An equilibrium phase separated ternary system of polystyrene (PS)/polydimethylsiloxane (PDMS)/p-xylene was prepared, and the PS-rich phase was dispersed as droplets in a matrix of the PDMS-rich phase. The system was placed between vertical electrodes and the droplets rotated around a vertical axis perpendicular to the electric field direction in 4–8-kV cm−1DC fields; in 2–4-kV cm−1, 0.1-Hz AC fields; and in 4-kV cm−1, 1-MHz AC fields, in some cases stopping, restarting, and changing the direction of rotation. They rotated less than a quarter of a turn back and forth in 1–10-Hz, 2–4-kV cm−1fields and did not rotate at all in 1-kHz fields. Rotational velocities measured in the DC field were in agreement with an existing theory; those measured in the 0.1-Hz AC field and estimated in the 1-MHz AC field were in direct disagreement with a different existing theoretical treatment. When the PDMS-rich droplets were dispersed into a matrix of the PS-rich phase, the droplets elongated in the field direction in a 2-kV/cm, 0.1-Hz electric field. Occasionally a portion of the matrix phase broke off into the PDMS-rich droplet, rotated for a while, and then rejoined the matrix phase.