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Mar 2008

Volume 20, Issue 3, Articles (03xxxx)

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Phys. Fluids 20, 035102 (2008); http://dx.doi.org/10.1063/1.2840200 (11 pages)

Karthik Duraisamy and Sanjiva K. Lele
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back to top Interfacial Flows

Hydrodynamic forces involving deformable interfaces at nanometer separations

Rogério Manica, Jason N. Connor, Raymond R. Dagastine, Steven L. Carnie, Roger G. Horn, and Derek Y. C. Chan

Phys. Fluids 20, 032101 (2008); http://dx.doi.org/10.1063/1.2839577 (12 pages) | Cited 19 times

Online Publication Date: 5 March 2008

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A model is developed to describe the dynamic forces acting between two deformable drops, or between one drop and a solid surface, when they are in relative axisymmetric motion at separations of ≲100 nm in a Newtonian liquid. Forces arise from hydrodynamic pressure in the draining liquid film that separates the interfaces and from disjoining pressure due to repulsive or attractive surface forces. Predictions of the model are successfully compared with recent experimental measurements of the force between two micrometer-scale surfactant stabilized decane drops in water in an atomic force microscope [ S. L. Carnie, D. Y. C. Chan, C. Lewis, R. Manica, and R. R. Dagastine, Langmuir 21, 2912 (2005) ; R. R. Dagastine, R. Manica, S. L. Carnie, D. Y. C. Chan, G. W. Stevens, and F. Grieser, Science 313, 210 (2006) ] and with subnanometer resolution measurements of time-dependent deformations of a millimeter-scale mercury drop approaching a flat mica surface in a modified surface force apparatus [ J. N. Connor and R. G. Horn, Faraday Discuss. 123, 193 (2003) ; R. G. Horn, M. Asadullah, and J. N. Connor, Langmuir 22, 2610 (2006) ]. Special limits of the model applicable to small and moderate deformation regimes are also studied to elucidate the key physical ingredients that contribute to the characteristic behavior of dynamic collisions involving fluid interfaces.
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47.55.dd Bubble dynamics
47.55.dr Interactions with surfaces
68.35.Md Surface thermodynamics, surface energies

A thin conducting viscous film on an inclined plane in the presence of a uniform normal electric field: Bifurcation scenarios

B. Uma and R. Usha

Phys. Fluids 20, 032102 (2008); http://dx.doi.org/10.1063/1.2896300 (17 pages) | Cited 3 times

Online Publication Date: 27 March 2008

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A theory for two dimensional long and stationary waves of finite amplitude on a thin viscous liquid film down an inclined plane in the presence of uniform electric field at infinity is investigated. A set of exact averaged equations for the film flow system is described and linearized stability analysis of the uniform flow is performed using normal-mode formulation and the critical condition for linear instability is obtained. The linearized instability for the permanent wave equation, consistent to the second order in ϵ, is examined and the eigenvalue properties of the fixed points are classified in various parametric regimes. Numerical integration of the permanent wave equation as a third-order dynamical system is carried out. Different bifurcation scenarios leading to multiple-hump solitary waves or leading to chaos are exhibited in the parametric space.
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47.20.Ky Nonlinearity, bifurcation, and symmetry breaking
47.35.-i Hydrodynamic waves
47.52.+j Chaos in fluid dynamics
47.65.-d Magnetohydrodynamics and electrohydrodynamics

Characterization of the electrosprays of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide in vacuum

Manuel Gamero-Castaño

Phys. Fluids 20, 032103 (2008); http://dx.doi.org/10.1063/1.2899658 (11 pages) | Cited 7 times

Online Publication Date: 31 March 2008

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The electrosprays of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide are composed of a complex mixture of ions and charged droplets, which can be analyzed to determine the structure of the beam and infer significant features of the electrohydrodynamic atomization. In particular, we use a combination of retarding potential and time of flight techniques to study these beams and are able to quantify the voltage drop along the cone jet, together with the velocity and diameter of the jet at the breakup location, confirm the strong influence of viscosity and electrification in the breakup, show that the electric field in and near the Taylor cone tip is insensitive to external electrostatic parameters, and study the spatial distribution of ions and droplets, whereby the paradoxical absence of ions in the outmost region of the beam is established. The research described in this article can be exploited in the modeling of capillary instability of charged jets: testing the results of these models is difficult, especially when nanojets are involved, and our findings and techniques provide the experimental support required by the theoretical activity. The present research is also applicable to the modeling of colloid thruster beams.
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47.57.jd Electrokinetic effects
47.55.df Breakup and coalescence
47.60.Kz Flows and jets through nozzles
47.65.-d Magnetohydrodynamics and electrohydrodynamics
47.20.-k Flow instabilities
41.20.Cv Electrostatics; Poisson and Laplace equations, boundary-value problems
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