Pattern formation of chevrons in the conduction regime in homeotropically aligned liquid crystals

Huh, Jong–Hoon; Hidaka, Yoshiki; Rossberg, Axel G.; Kai, Shoichi

doi:10.1103/physreve.61.2769

Cited by 60 publications

(37 citation statements)

References 38 publications

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“…Conductive normal rolls, dielectric rolls and the prewavy pattern may follow each other with increasing f (dielectric rolls may be skipped in compounds with higher conductivity). Near the crossover frequency f c , the conductive (or dielectric) rolls can coexist with the prewavy pattern resulting in the defect-free chevron structure [51].…”

Section: Figurementioning

confidence: 99%

Convective Patterns in Liquid Crystals Driven by Electric Field

Buka

Éber

Pesch

et al. 2006

NATO Science Series II: Mathematics, Physics and Chemistry

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A systematic overview of various electric-field induced pattern forming instabilities in nematic liquid crystals is given. Particular emphasis is laid on the characterization of the threshold voltage and the critical wavenumber of the resulting patterns. The standard hydrodynamic description of nematics predicts the occurrence of striped patterns (rolls) in five different wavenumber ranges, which depend on the anisotropies of the dielectric permittivity and of the electrical conductivity as well as on the initial director orientation (planar or homeotropic). Experiments have revealed two additional pattern types which are not captured by the standard model of electroconvection and which still need a theoretical explanation.

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Section: Figurementioning

confidence: 99%

Convective Patterns in Liquid Crystals Driven by Electric Field

Buka

Éber

Pesch

et al. 2006

NATO Science Series II: Mathematics, Physics and Chemistry

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“…[1][2][3] A wide range of EC investigations have been carried out using planar [4][5][6][7][8][9][10] and homeotropic [11][12][13][14] nematic alignment; in this work we are interested in the planar configuration. The EC process is in some respects the anisotropic counterpart of Rayleigh-Bénard convection (RBC), with the EC electric field replacing the vertical thermal gradient in RBC.…”

Section: Introductionmentioning

confidence: 99%

Dynamics of laser-induced electroconvection pulses

et al. 2004

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We first report that, for planar nematic MBBA, the electroconvection threshold voltage has a nonmonotonic temperature dependence, with a well-defined minimum, and a slope of about -0.12 V/degree near room temperature. Motivated by this observation, we have designed an experiment in which a weak continuous-wave absorbed laser beam with a diameter comparable to the pattern wavelength generates a locally supercritical region, or pulse, in dyedoped MBBA. Working 10-20% below the laser-free threshold voltage, we observe a steadystate pulse shaped as an ellipse with the semimajor axis oriented parallel to the nematic director, with a typical size of several wavelengths. The pulse is robust, persisting even when spatially extended rolls develop in the surrounding region, and displays rolls that counterpropagate along the director at frequencies of tenths of Hz, with the rolls on the left (right) side of the ellipse moving to the right (left). Systematic measurements of the samplevoltage dependence of the pulse amplitude, spatial extent, and frequency show a saturation or decrease when the control parameter (evaluated at the center of the pulse) approaches ∼ 0.3.We propose that the model for these pulses should be based on the theory of control-parameter ramps, supplemented with new terms to account for the advection of heat away from the pulse when the surrounding state becomes linearly unstable. The advection creates a negative feedback between the pulse size and the efficiency of heat transport, which we argue is responsible for the attenuation of the pulse at larger control-parameter values.

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“…Recently another type of chevrons -the 'defect free' chevrons [25] -has also been identified in the 'conductive' regime. Though their main characteristics are very similar to the ordinary -'defect mediated' -chevrons, there are no defects at the domain boundaries; rather the rolls seem to have a curvature (figure 6c).…”

Section: Patterns Of Large Wavelengthmentioning

confidence: 99%

Electroconvection in homeotropic nematic liquid crystals

Éber

Buka

2005

Phase Transitions

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Electroconvection is a classical example of pattern-forming phenomena in liquid crystals, typically observed in nematics with negative dielectric and positive conductivity anisotropies. This article focuses on how electroconvection in the homeotropic geometry differs from that in planar alignment. The influence of an additional magnetic field on the pattern characteristics and on secondary instabilities (the normal roll-abnormal roll transition) is discussed. The homeotropic alignment offers unique possibilities also for studying defect motion. Basic characteristics of some patterns of large wavelength are presented and compared with those of the classical Carr-Helfrich structures. Finally, electroconvection in substances with negative conductivity anisotropy is addressed.

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Pattern formation of chevrons in the conduction regime in homeotropically aligned liquid crystals

Cited by 60 publications

References 38 publications

Convective Patterns in Liquid Crystals Driven by Electric Field

Convective Patterns in Liquid Crystals Driven by Electric Field

Dynamics of laser-induced electroconvection pulses

Electroconvection in homeotropic nematic liquid crystals

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