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SUMMARY:Electrohydrodynamics of particles and drops in strong electric fie
 lds - Debasish Das (DAMTP\, University of Cambridge)
DTSTART:20170118T130000Z
DTEND:20170118T140000Z
UID:TALK70151@talks.cam.ac.uk
CONTACT:Julius Bier Kirkegaard
DESCRIPTION:The dynamics of dielectric rigid particles and liquid drops su
 spended in another liquid medium and subject to a uniform DC electric fiel
 d\, the study of which forms the field of electrohydrodynamics (EHD)\, has
  fascinated scientists for decades. This phenomenon is described by the mu
 ch celebrated Melcher-Taylor leaky dielectric model. The model hypothesise
 s development of interfacial charge on the application of an electric fiel
 d and prescribes a balance between transient charge\, jump in normal Ohmic
  currents due to finite conductivities of the medium and charge convection
  arising from interfacial velocity. While there have been numerous studies
  on the dynamics of particles and drops more conducting than the surroundi
 ng liquid medium\, weakly conducting particles and drops in strong electri
 c fields\, known to undergo symmetry- breaking bifurcations leading to ste
 ady rotation known as Quincke electrorotation\, have received much less at
 tention. Recent experiments have reported a decrease in the effective visc
 osity of particle under Quincke rotation\, thereby providing a means to tu
 ne the rheological properties of these suspensions. However\, existing mod
 els based on an isolated particle\, valid for dilute suspensions\, have be
 en shown to be inaccurate as the density of particles increases. Motivated
  to resolve these discrepancies\, we develop a theoretical model to accoun
 t for electrohydrodynamic interactions between a pair of spherical particl
 es. We then turn our attention to many particles free to roll on an electr
 ode due to Quincke rotation. Using numerical simulations\, we show that el
 ectrohydrodynamic interactions between particles give rise to collective m
 otion of these colloidal suspensions. We find emergence of a polar liquid 
 state with a large vortical structure in circular confinement. Finally\, w
 e address the problem of electrohydrodynamics of deformable liquid drops\,
  first studied by Taylor in 1966. We develop a transient small deformation
  theory for axisymmetric drops while including the nonlinear charge convec
 tion term neglected by previous researchers. We also use numerical simulat
 ions based on a novel three-dimensional boundary element method to capture
  large deformations. These simulations are the first to capture Quincke ro
 tation due to inclusion of the nonlinear charge convection term and show e
 xcellent agreement with existing experimental data and theoretical predict
 ions in the small deformation regime.
LOCATION:MR11\, Centre for Mathematical Sciences\, Wilberforce Road\, Camb
 ridge
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