(128e) Effect Of Surfactant On Drop Dynamics In Electric Fields

Surfactants modify interfacial properties and significantly affect drop behavior in electric fields. I study the dynamics of a drop, which is covered with a dilute monolayer of insoluble surfactant, in DC and AC electric fields. The problem is challenging because drop shape and surfactant distribution are not given a priori but are governed by the balance between interfacial, fluid and electric stresses. I will present theoretical analyses based on the Taylor leaky dielectric model that quantitatively describe the behavior of a surfactant-covered drop in uniform electric fields, e.g. drop deformation and rotation. The results show that the type of stationary shape, oblate or prolate, is controlled by the conductivity and dielectric constant ratios. However, in contrast to surfactant-free drops, the deformation of a surfactant-covered drop is independent of the viscosity ratio because Marangoni stresses immobilize the interface and suppress the electro-hydrodynamic flow.