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1. Deformation and Breakup of Conducting Drops under Uniform Electric Fields 

A conducting drop suspended in a viscous dielectric and subjected to a uniform DC electric field deforms to a steady-state shape when the electric stress and the viscous stress balance. Beyond a critical electric capillary number Ca, which is the ratio of the electric to the capillary stress, a drop undergoes breakup. Although the steady-state deformation is independent of the viscosity ratio λ of the drop and the medium phase, the breakup itself is dependent upon λ and Ca. We perform a detailed experimental and numerical analysis of the axisymmetric shape prior to breakup (ASPB), which explains that there are three different kinds of ASPB modes: the formation of lobes, pointed ends and non-pointed ends. The axisymmetric shapes undergo transformation into the non-axisymmetric shape at breakup (NASB) before disintegrating. It is found that the lobes, pointed ends and non-pointed ends observed in ASPB give way to NASB modes of charged lobes disintegration, regular jets (which can undergo a whipping instability) and open jets, respectively. A detailed experimental and numerical analysis of the ASPB modes is conducted that explains the origin of the experimentally observed NASB modes. Several interesting features are reported for each of the three axisymmetric and non-axisymmetric modes when a drop undergoes breakup.

References:

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1. Rahul Karyappa, Shivraj Deshmukh and Rochish Thaokar, Breakup of a conducting drop in a uniform electric field, Journal of Fluid   

    Mechanics, 754, 550-589 (2014). DOI: 10.1017/jfm.2014.402

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2. Electroemulsification in a Uniform Electric Field 

Emulsification using electric fields is an easy alternative to flow-induced drop breakup, and the former is reported to be more effective and economical than the latter, especially when the medium phase is poorly conducting and highly viscous. The emulsification of a coarse water-in-oil emulsion in a uniform electric field is studied. We perform a detailed experimental analysis of the effect of applied electric field strength and the duration of the applied electric field on the drop size distribution. The average diameter, as well as the time for emulsification, decreases with an increase in the intensity of the electric field. Moreover, narrow size distribution is observed. The average size of a few microns of the dispersed phase could be achieved. New breakup mechanisms at play in the emulsification process are discussed. Identified mechanisms involve charged lobe disintegration, charged drop breakup, chain formation in which several water droplets are interconnected by thin water bridges, electrospraying and charge transfer, and coalescence. The study shows that charged drop disintegration could be the key mechanism of fine emulsification of an initially electrically neutral coarse emulsion.

References:

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1. Rahul Karyappa, Ankita Naik and Rochish Thaokar, Electroemulsification in a uniform electric field, Langmuir, 32, 46-54   

    (2015). DOI: 10.1021/acs.langmuir.5b03188

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