Velocity and current measurements in electroconvecting smectic films

Morris, Stephen W.; Bruyn, John R. de; May, A. D.

doi:10.1103/physreva.44.8146

Cited by 34 publications

(53 citation statements)

References 38 publications

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“…This extra coupling formally distinguishes the resulting equations from those of thermal convection in the Rayleigh-Bénard problem, although some interesting similarities remain. The value of the critical wavenumber from the linear stability analysis [8] is in good agreement with experiment [4,5,7].…”

Section: Introductionsupporting

confidence: 80%

“…In what follows, we consider only very thin isotropic films, relevant to the case of smectic A, on which most of the experiments have been performed. [4][5][6][7] A theoretical model of the onset of electroconvection in suspended films was introduced by Daya, Morris, and de Bruyn. [8] The film was represented as a weakly conducting, twodimensional, isotropic fluid.…”

Section: Introductionmentioning

confidence: 99%

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Weakly nonlinear analysis of electroconvection in a suspended fluid film

Deyirmenjian¹,

Daya²,

Morris³

1997

Phys. Rev. E

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It has been experimentally observed that weakly conducting suspended films of smectic liquid crystals undergo electroconvection when subjected to a large enough potential difference. The resulting counter-rotating vortices form a very simple convection pattern and exhibit a variety of interesting nonlinear effects. The linear stability problem for this system has recently been solved. The convection mechanism, which involves charge separation at the free surfaces of the film, is applicable to any sufficiently two-dimensional fluid.In this paper, we derive an amplitude equation which describes the weakly nonlinear regime, by starting from the basic electrohydrodynamic equations. This regime has been the subject of several recent experimental studies. The lowest order amplitude equation we derive is of the Ginzburg-Landau form, and describes a forward bifurcation as is observed experimentally. The coefficients of the amplitude equation are calculated and compared with the values independently deduced from the linear stability calculation.

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Section: Introductionsupporting

confidence: 80%

Section: Introductionmentioning

confidence: 99%

Weakly nonlinear analysis of electroconvection in a suspended fluid film

Deyirmenjian¹,

Daya²,

Morris³

1997

Phys. Rev. E

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“…Almost all the experiments performed in the rectangular geometry had Λ < ∼ 10 [20][21][22][23][24] and were well-modelled by the theory for an unbounded strip for which Λ = ∞. It is thus resonable to expect g at α = 0.80 to be close to its limiting value for α = 1.…”

Section: Coefficients Of the Cubic Nonlinearity Without Shearmentioning

confidence: 99%

“…As in previous experiments [3,6,[20][21][22][23][24], our study used smectic A octylcyanobiphenyl (8CB). 8CB has a smectic A phase between 21…”

Section: A the Liquid Crystalmentioning

confidence: 99%

Bifurcations in annular electroconvection with an imposed shear

2001

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We report an experimental study of the primary bifurcation in electrically-driven convection in a freely suspended film. A weakly conducting, submicron thick smectic liquid crystal film was supported by concentric circular electrodes. It electroconvected when a sufficiently large voltage V was applied between its inner and outer edges. The film could sustain rapid flows and yet remain strictly two-dimensional. By rotation of the inner electrode, a circular Couette shear could be independently imposed. The control parameters were a dimensionless number R, analogous to the Rayleigh number, which is ∝ V 2 and the Reynolds number Re of the azimuthal shear flow. The geometrical and material properties of the film were characterized by the radius ratio α, and a dimensionless number P, analogous to the Prandtl number. Using measurements of current-voltage characteristics of a large number of films, we examined the onset of electroconvection over a broad range of α, P and Re. We compared this data quantitatively to the results of linear stability theory. This could be done with essentially no adjustable parameters. The current-voltage data above onset were then used to infer the amplitude of electroconvection in the weakly nonlinear regime by fitting them to a steady-state amplitude equation of the Landau form. We show how the primary bifurcation can be tuned between supercritical and subcritical by changing α and Re.

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“…For example, the standard case of buoyancy-driven Rayleigh-Bénard convection (RBC) has been studied in the presence of rotation [7,8,9,10] and shearing due to an open throughflow [11,12], as well as in the geophysically interesting cases of radial gravitation with rotation [5,6]. The phenomenology of two-dimensional (2D) electroconvection in a rectangular geometry was the subject of our previous experimental [13,14,15,16,17] and theoretical [2,3] work. These studies made precise the degree of analogy with RBC; the electrical nature of the forcing introduces some crucial differences in detail, even at the level of linear stability.…”

Section: Introductionmentioning

confidence: 99%

Electrically driven convection in a thin annular film undergoing circular Couette flow

1999

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We investigate the linear stability of a thin, suspended, annular film of conducting fluid with a voltage difference applied between its inner and outer edges. For a sufficiently large voltage, such a film is unstable to radially-driven electroconvection due to charges which develop on its free surfaces. The film can also be subjected to a Couette shear by rotating its inner edge. This combination is experimentally realized using films of smectic A liquid crystals. In the absence of shear, the convective flow consists of a stationary, azimuthally one-dimensional pattern of symmetric, counter-rotating vortex pairs. When Couette flow is applied, an azimuthally traveling pattern results. When viewed in a co-rotating frame, the traveling pattern consists of pairs of asymmetric vortices. We calculate the neutral stability boundary for arbitrary radius ratio α and Reynolds number Re of the shear flow, and obtain the critical control parameter Rc (α, Re) and the critical azimuthal mode number mc (α, Re). The Couette flow suppresses the onset of electroconvection, so that Rc (α, Re) > Rc (α, 0). The calculated suppression is compared with experiments performed at α = 0.56 and 0 ≤ Re ≤ 0.22. Fluids, 11, 3613 (1999). See also http://mobydick.physics.utoronto.ca. Physics of

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Velocity and current measurements in electroconvecting smectic films

Cited by 34 publications

References 38 publications

Weakly nonlinear analysis of electroconvection in a suspended fluid film

Weakly nonlinear analysis of electroconvection in a suspended fluid film

Bifurcations in annular electroconvection with an imposed shear

Electrically driven convection in a thin annular film undergoing circular Couette flow

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