Hydrodynamics of Liquid Crystals

Forster, Dieter; Lubensky, T. C.; Martin, Paul C.; Swift, J. B.; Pershan, Peter S.

doi:10.1103/physrevlett.26.1016

Cited by 263 publications

(137 citation statements)

References 14 publications

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“…This process has been studied in detail by Bacri [7,8] angle between the director and the acoustical wave vector is well described by the hydrodynamic theory proposed by Forster et al [9].…”

mentioning

confidence: 97%

Ultrasonic investigation of nematic liquid crystals in the isotropic and nematic phases

Nagai¹,

Martinoty²,

Candau³

1976

J. Phys. France

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Resumé. 2014 Nous avons mesuré la variation en fonction de la fréquence de l'atténuation ultrasonore d'un cristal liquide nématique, le n-pentyl cyanobiphényle, au voisinage de la transition nématique-isotrope. Les Abstract. 2014 We report measurements of the frequency dispersion of ultrasonic attenuation for a nematic liquid crystal, the n-pentyl cyanobiphenyl in the vicinity of the nematic-isotropic transition. In the isotropic phase, the experimental results are well described by the theory recently proposed by Imura and Okano. The frequency 03C9max at which the maximum of attenuation per wave length 03B103BB occurs, as well as the peak value (03B103BB) max, diverge at the transition with the critical exponents predicted by the theory.We have extended the Imura-Okano theory to the nematic phase on the basis of a coupling between sinusoidal temperature variation induced by sound wave and the elastic Frank constants. This model accounts semi-quantitatively for the experimental results.We have also investigated the dependence of the low frequency attenuation with respect to the angle between the director and the acoustical wave-vector for a nematic liquid crystal (Merck V) which exhibits a broad mesomorphic range. Far below the transition temperature the experimental data are well described by the theory of Forster et al., provided that the frequencies are far below the intramolecular relaxational frequency.

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mentioning

confidence: 97%

Ultrasonic investigation of nematic liquid crystals in the isotropic and nematic phases

Nagai¹,

Martinoty²,

Candau³

1976

J. Phys. France

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“…no divv terms are left in the stress tensor (and thus in the boundary conditions). This leads to [17,19] ν 2 = ν 4 and ν 5 = 0. These are purely formal relations, which generally have no correspondence to reality (for isotropic fluids this procedure would give ζ = 2ν/3, which again is far off the experimental values).…”

Section: Incompressible Uniaxial Nematicsmentioning

confidence: 99%

“…Note that the flow alignment and the back flow effect come with the same material parameter ensuring that they cancel each other in the entropy production, which is required by their (time) reversible character. The viscosity tensor reflects the uniaxial symmetry of nematics and reads in the notation of [19] …”

Section: Compressible Uniaxial Nematicsmentioning

confidence: 99%

Incompressibility conditions in liquid crystals

Pleiner

Brand

2002

Continuum Mechanics and Thermodynamics

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We discuss the implications of the incompressibility approximation on the number of relevant transport parameters, like viscosities, flow alignment coefficients, and rotational viscosities in uniaxial and biaxial nematic liquid crystals. A comparison between the hydrodynamic and the Leslie-Ericksen approach is given. Agreement is found, if in the latter description a redefinition of the pressure is assumed. For systems with positional order, like smectic and columnar liquid crystals and crystals, we show that, generally, incompressibility does not imply that the displacement field is source-free.

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“…However, a microscopic approach, was undertaken by the Harvard group using correlation functions. Later, this was extended to other mesomorphic phases using a macroscopic formalism [109][110][111]. The equivalence of these two different approaches was established by de Gennes [6].…”

Section: Flow Of Nematic Liquid Crystals: Nematodynamicsmentioning

confidence: 99%

Nematic Liquid Crystals and Nematic Colloids in Microfluidic Environment

Sengupta

Herminghaus

Bahr

2011

Molecular Crystals and Liquid Crystals

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Where the mind is without fear and the head is held high;Where knowledge is free;Where the world has not been broken up into fragments by narrow domestic walls;Where words come out from the depth of truth;Where tireless striving stretches its arms towards perfection;Where the clear stream of reason has not lost its way into the dreary desert sand of dead habit;Where the mind is led forward by thee into ever-widening thought and actionInto that heaven of freedom, my Father, let my country awake.Rabindranath Tagore (1861Tagore ( -1941 To my parents, my brother, and all the sacrifices they made for me AbstractThe doctoral thesis presented here is one of the first systematic attempts to unravel the wonderful world of liquid crystals within microfluidic confinements, typically channels with dimensions of tens of micrometers. The present work is based on experiments with a roomtemperature nematic liquid crystal, 5CB, and its colloidal dispersions within microfluidic devices of rectangular cross-section, fabricated using standard techniques of soft lithography. To begin with, a combination of physical and chemical methods was employed to create well defined boundary conditions for investigating the flow experiments. The walls of the microchannels were functionalized to induce different kinds of surface anchoring of the 5CB molecules: degenerate planar, uniform planar, and homeotropic surface anchoring. Channels possessing composite anchoring conditions (hybrid) were additionally fabricated, e. g. homeotropic and uniform planar anchoring within the same channel. On filling the microchannels with 5CB in the isotropic phase, different equilibrium configurations of the nematic director resulted, as the sample cooled down to nematic phase. For a given surface anchoring, the equilibrium director configuration varied also with the channel aspect ratio. The static director field within the channel registered the initial conditions for the flow experiments. The static and i ii dynamic experiments have been analyzed using a combination of polarization, and confocal fluorescence microscopy techniques, along with particle tracking method for measuring the flow speeds. Additionally, dual-focus fluorescence correlation spectroscopy is introduced as a generic velocimetry tool for liquid crystal flows.The flow of nematic liquid crystals is inherently complex due to the coupling between the flow and the nematic director. The presence of the four confining walls and the nature of surface anchoring on them complicate the flow-director interactions further. In microchannels possessing degenerate planar anchoring, four different flow-induced defect textures were identified with increasing Ericksen number: π-walls, disclination lines pinned to the channel walls, disclination lines with one pinned and one freely suspended end, and disclination loops freely flowing in a chaotic manner. However, such textures and sequence of defects were not observed for flows within channels with homogeneous anchoring.Using experiments and numerical modeling...

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Hydrodynamics of Liquid Crystals

Cited by 263 publications

References 14 publications

Ultrasonic investigation of nematic liquid crystals in the isotropic and nematic phases

Ultrasonic investigation of nematic liquid crystals in the isotropic and nematic phases

Incompressibility conditions in liquid crystals

Nematic Liquid Crystals and Nematic Colloids in Microfluidic Environment

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