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Electro-deformation of a surfactant-laden viscous drop

Yuan-Nan Young (New Jersey Inst. Tech.), Herve Nganguia (NJIT), Petia Vlahovska (Brown University), Hao Lin (Rutgers University)

Electrohydrodynamics and electrokinetics of fluid systems

Mon 4:20 - 5:40

Barus-Holley 161

In this work we investigate the electro-deformation of a viscous drop covered with non-diffusing insoluble surfactant under a DC electric field in the Taylor-Melcher leaky dielectric framework. We use (1) a second-order small-deformation analysis and (2) a spheroidal model for a highly deformed (prolate or oblate) drop. Both approaches are validated by comparing against experimental data and numerical simulation results in the literature. By comparing these two models we establish the range of validity for the small-deformation analysis. We find that non-diffusing insoluble surfactant completely suppresses the fluid flow at equilibrium and consequently the distinction between the two prolate modes. Detailed analysis of results from the spheroidal model shows that surfactant effects, such as tip-stretching and surface dilution effects, are more prominent at large electric capillary number. These surfactant effects can be well captured in our spheroidal model, but cannot be described in the second-order small-deformation theory. In addition we find that Marangoni stress is important for both prolate and oblate drops at high capillary number. We also examine how the surfactant may affect the critical capillary number.