Pattern formation in a liquid crystal

Rehberg, Ingo; Winkler, B. L.; Juárez, Manuel de la Torre; Rasenat, S.; Schöpf, Wolfgang

doi:10.1007/bfb0108006

Cited by 48 publications

(26 citation statements)

References 8 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%

“…14) Some very recent work on these systemg is discussed elsewhere in these proceedings. 4 Secondary instabilities occur in all these systems when they are driven further from equilibrium, (2-5~ which leads to complex, often time-varying, threedimensional flow and eventually to turbulence.…”

Section: Introductionmentioning

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%

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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%

Section: Introductionmentioning

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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“…For electroconvection (an anisotropic system), two main classes of patterns occur as the initial transition: normal and oblique rolls [14,15,16]. Electroconvection uses a nematic liquid crystal.…”

Section: Introductionmentioning

confidence: 99%

Dislocation dynamics in an anisotropic stripe pattern

2004

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The dynamics of dislocations confined to grain boundaries in a striped system are studied using electroconvection in the nematic liquid crystal N4. In electroconvection, a striped pattern of convection rolls forms for sufficiently high driving voltages. We consider the case of a rapid change in the voltage that takes the system from a uniform state to a state consisting of striped domains with two different wavevectors. The domains are separated by domain walls along one axis and a grain boundary of dislocations in the perpendicular direction. The pattern evolves through dislocation motion parallel to the domain walls. We report on features of the dislocation dynamics. The kinetics of the domain motion are quantified using three measures: dislocation density, average domain wall length, and the total domain wall length per area. All three quantities exhibit behavior consistent with power law evolution in time, with the defect density decaying as t −1/3 , the average domain wall length growing as t 1/3 , and the total domain wall length decaying as t −1/5 . The two different exponents are indicative of the anisotropic growth of domains in the system.

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“…That instability is of interest in many physical problems and has been observed experimentally in, e.g. binary ñuid convection [2][3][4][5], isothermal double diffusive convection [6], puré Rayleigh-Bénard convection (as a secondary instability of rolls) [7][8][9], the Taylor-Couette system [10,11], several thermocapillary flows [12][13][14], electrodynamic convection in nematic liquid crystals [15][16][17][18], and several combustión systems [19][20][21].…”

Section: Introductionmentioning

confidence: 99%