Hydrodynamic instabilities of nematic liquid crystals under A. C. electric fields

Dubois‐Violette, E.; Gennes, P. G. de; Parodi, O.

doi:10.1051/jphys:01971003204030500

Cited by 297 publications

(92 citation statements)

References 12 publications

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“…(7) The theory of electroconvection has been studied in much detail in nematic liquid crystals in the case where the mechanism driving the instability involves the anisotropy of the material. (4)(5)(6)(7)(8)(9) In this case, terms must be included which describe the coupling of the flow to the director and hence to the axes of the tensor material parameters. These are not necessary in our case because our flow does not couple to the director.…”

Section: Discussionmentioning

confidence: 99%

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Patterns at the onset of electroconvection in freely suspended smectic films

Morris¹,

Bruyn²,

May³

1991

J Stat Phys

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We report the results of experiments on electrically driven convection that occurs in a thin, freely suspended film of smectic A liquid crystal when an electric field is applied in the plane of the film. Convection in a vortex pattern is found above a well-defined critical voltage. The film behaves as a twodimensional isotropic liquid: neither its thickness nor the director field are modified by the flow. We present measurements of the critical voltage at the onset of convection in two experimental configurations--one which allows the injection of charges into the film from the electrodes, and one which does not. When injection is present, the critical voltage for the onset of flow increases monotonically with increasing frequency of applied field. With no injection, there is no instability at DC and the critical voltage diverges there. The nature of the flow pattern observed at onset changes with frequency. Below a certain frequency the film flows in vortices that extend over the width of the film; above this frequency the flow is confined to two lines of smaller vortices localized along the electrodes. We present a simple discussion of the mechanisms which drive the convection.

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Section: Discussionmentioning

confidence: 99%

“…(17) Electroconvention of the Williams domain type, which is observed in certain nematics, is driven by the Carr-Helfrich (4)(5)(6)(7)(8)(9) mechanism. This mechanism is usually found in materials with a negative dielectric anisotropy and necessarily involves a reorientation of the director.…”

Section: Introductionmentioning

confidence: 99%

Patterns at the onset of electroconvection in freely suspended smectic films

Morris¹,

Bruyn²,

May³

1991

J Stat Phys

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“…For instance in a nematic layer subjected to an electric field normal to it, a periodic modulation of the molecular axis can be produced which is then coupled to a convective flow [10]. The [11,13].…”

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confidence: 99%

Hydrodynamic transitions to chaos in the convection of an anisotropic fluid

1986

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Abstract. -We present the first spontaneous sequence of hydrodynamic instabilities due to the evolution of the convective flow from the rest state toward chaos in an anisotropic fluid : a nematic liquid crystal subjected to an AC electric field. The resulting structures are of decreasing symmetry as the control parameter is gradually increased. The study of the streamlines allows the interpretation of the entire sequence by the evolution of the convective flow up to the onset of chaos. We show that the first important step in the flow evolution is the build up of a second mode of rotation which is associated with a pinching instability of the vortex lines. A simple picture is then proposed in order to describe the essential steps of a possible route to chaos, and which could be extended to other convective systems.

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“…In agreement with theoretical expectations the wavelength decreases with increasing frequency. The observed deviation from the approximate λ ∼ ω −1/2 law at the highest frequencies indicates that the wavelength has reached the Debye length and charge diffusion effects need to be taken into account in the theoretical description, an effect noticed already by Dubois-Violette et al [11] (and typically to be expected at the ∼ 10 2 fold cutoff frequency [17]). …”

Section: Localized Bulk Modes In the Standard Modelmentioning

confidence: 89%

“…The SM predicts bulk convection. It has, on the linear level, been worked out by Dubois-Violette et al [11]. Later it was modified for square-wave driving voltages [12] and to include flexoelectric effects [13][14][15] and the effects of finite cell thickness [16].…”

Section: Introductionmentioning

confidence: 99%

Twist localizes three-dimensional patterns

Rossberg

2000

Phys. Rev. E

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A mechanism for the localization of spatially periodic, self-organized patterns in anisotropic media which requires systems extended in all three spatial dimensions is presented: When the anisotropy axis is twisted the pattern becomes localized in planes parallel to the anisotropy axis. An analytic description of the effect is developed and used to interpret recent experiments in the high-frequency regime of electroconvection by Bohatsch and Stannarius [Phys. Rev. E 60, 5591 (1999)]. The localization width is found to be of the order of magnitude of the geometrical average of pattern wavelength and the inverse twist. 45.70.Qj, 47.54.+r, 83.70.Jr, 44.27.+g

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Hydrodynamic instabilities of nematic liquid crystals under A. C. electric fields

Cited by 297 publications

References 12 publications

Patterns at the onset of electroconvection in freely suspended smectic films

Patterns at the onset of electroconvection in freely suspended smectic films

Hydrodynamic transitions to chaos in the convection of an anisotropic fluid

Twist localizes three-dimensional patterns

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