Viscosity coefficients of partially aligned nematic and nematic discotic liquid crystals

Ehrentraut, H.; Hess, Siegfried

doi:10.1103/physreve.51.2203

Cited by 92 publications

(90 citation statements)

References 22 publications

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“…The value of ͑h 1 -h 2 ͒͞g 1 is within 10% of unity and has a value of 0.97 for the modified set of viscosity coefficients, thus agreeing with predictions based on ellipsoidal molecules [16]. In addition, the general rule derived from microscopic models [17] that for nematic liquid crystals, h 1 . g 1 .…”

Section: -2supporting

confidence: 64%

Direct Optical Quantification of Backflow in a90°Twisted Nematic Cell

2002

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Optical guided mode observations of the transient director profile (optical tensor distribution) during the relaxation of a 90 ± twisted nematic cell directly reveals backflow. In the first 6 ms of the relaxation process, after a voltage across the cell is removed, the midplane tilt of the director increases, reaching a maximum value of 101 ± at 1.4 ms. This increase in midplane tilt is attributed to coupling between fluid flow (backflow) and director reorientation. A 270 ± twisted state of the opposite handedness to the 90 ± twisted state found at equilibrium is shown to exist during the backflow period. Good fits of theoretical models with experimentally determined time dependent director profiles yield the viscosity coefficients.

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Section: -2supporting

confidence: 64%

Direct Optical Quantification of Backflow in a90°Twisted Nematic Cell

2002

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“…The theory of Kuzuu and Doi [36] for rodlike molecules predicts a value of α < 0.004 over the entire nematic range. An affine transformation theory [37,38] predicts values α < 0.1 for molecules of elongation κ ≥ 3 at modest nematic order parameters, and α ≡ 0 in the perfectly aligned limit.…”

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confidence: 99%

Propagating Director Bend Fluctuations in Nematic Liquid Crystals

Humpert

Allen

2015

Phys. Rev. Lett.

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We show, by molecular simulation, that for a range of standard, coarse-grained, nematic liquid crystal models, the director bend fluctuation is a propagating mode. This is in contrast to the generally-accepted picture of nematic hydrodynamics, in which all the director modes (splay, twist, bend, and combinations thereof) are overdamped. By considering the various physical parameters that enter the equations of nematodynamics, we propose an explanation of this effect, and conclude that propagating bend fluctuations may be observable in some experimental systems.

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“…Viscous anisotropies are well characterized experimentally [21][22][23][24] and theoretically [25]. One prominent example here is the ordering in magnitude of the three Miesowicz shear viscosities, where the largest flow resistance is obtained when the average molecular orientation is fixed along the velocity gradient direction and the smallest when the average molecular orientation is fixed along the vorticity.…”

Section: Introductionmentioning

confidence: 98%

Theory of surface excess Miesowicz viscosities of planar nematic liquid crystal-isotropic fluid interfaces

Rey

2000

Eur. Phys. J. E

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An expression for the surface excess stress tensor for planar compressible interfaces between rodlike nematic liquid crystals and isotropic viscous fluids is derived using the classical surface excess theory formalism, adapted to capture the intrinsic anisotropy of the nematic orientational ordering. A required step in the theory is to find the actual stress tensor in the three-dimensional interfacial region, which is obtained by a decomposition of the kinematic fields (rate of deformation tensor and director Jaumann derivative) into tangential, normal, and mixed components with respect to the interface. The viscosity coefficients appearing in the surface excess stress tensor are expressed in terms of interfacial and bulk viscosities for planar, constant orientation, flows. The expressions are used to define the three fundamental surface excess Miesowicz shear viscosities, in analogy with the three bulk Miesowicz shear viscosities. The ordering in the magnitudes of the surface excess Miesowicz shear viscosities is shown to depend on the magnitude of the surface scalar nematic order parameter relative to that of the adjoining bulk nematic phase. When the surface scalar order parameter is greater than in the bulk, the classical ordering in terms of magnitudes of the three bulk Miesowicz shear viscosities is recovered. On the other hand, when the surface scalar order parameter is smaller than in the bulk, the classical ordering in terms of magnitudes of the three viscosities does not hold, and inequality transitions are predicted as the surface scalar order parameter increases towards the bulk value.PACS. 61.30.Cz Theory and models of liquid crystal structure -68.10.Et Interface elasticity, viscosity, and viscoelasticity -68.10.Cr Surface energy (surface tension, interface tension, angle of contact, etc.)

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Viscosity coefficients of partially aligned nematic and nematic discotic liquid crystals

Cited by 92 publications

References 22 publications

Direct Optical Quantification of Backflow in a90°Twisted Nematic Cell

Direct Optical Quantification of Backflow in a90°Twisted Nematic Cell

Propagating Director Bend Fluctuations in Nematic Liquid Crystals

Theory of surface excess Miesowicz viscosities of planar nematic liquid crystal-isotropic fluid interfaces

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