Flow Instabilities in Nematics

Dubois‐Violette, E.; Manneville, Paul

doi:10.1007/978-1-4612-3994-9_4

Cited by 13 publications

(13 citation statements)

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“…The estimates made for typical values of material constants of LCs [16] have shown that this velocity is about six order smaller than the velocity at which the turbulence occurs. The estimates made for typical values of material constants of LCs [16] have shown that this velocity is about six order smaller than the velocity at which the turbulence occurs.…”

Section: Couette and Poiseuille Flows In Isotropic Liquids And Liquidmentioning

confidence: 86%

“…These parameters are defined as [16] Re ¼ rlv h ð3:2Þ So some common rheological effects, shear thinning, for example, were established for them too.…”

Section: Couette and Poiseuille Flows In Isotropic Liquids And Liquidmentioning

confidence: 99%

“…One can find a lot of original papers and some reviews [16,17] with a description on hydrodynamic instabilities in liquid crystals. We will shortly describe the most interesting results for Couette and Poiseuille flows.…”

Section: Hydrodynamic Instabilities In Couette and Poiseuille Steady mentioning

confidence: 99%

“…It is well known that in most cases intensive stationary flows (with high values of a shear rate s) produce the stable orientation of a director in the flow plane at the angle q flow ¼ arctan ffiffiffiffiffiffiffiffiffiffiffiffi ffi a 3 =a 2 p ð3:5Þ 48j 3 Flows of Anisotropic Liquids relative to the flow velocity v [16]. It holds for particular flows of different types [18] and all over the layer excluding for the thin boundary layers with the thickness x(s) defined as [19] x 2 ðsÞ ¼ K 2s…”

Section: Hydrodynamic Instabilities In Couette and Poiseuille Steady mentioning

confidence: 99%

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Flows of Anisotropic Liquids

2009

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j45 crystals, presented in Chapter 2. The connection between translation motions and the orientational ones described accordingly in terms of a velocity field v(r, t) and a director field n(r, t) can be considered as a fundamental physical property of liquid crystals. It is responsible for a number of specific phenomena existing in liquid crystal media. Some of them, such as various instabilities induced by electric fields in thin layers of nematic liquid crystals or backflow effects arising at the turning off electric fields are of great practical importance (Chapter 6).The connection between v(r, t) and n(r, t) also results in a number of linear and nonlinear phenomena in flows of liquid crystals. In general, liquid crystals show non-Newtonian rheological behavior. It means, for example, that apparent shear viscosity depends on the shear rate. At the same time, strong magnetic (electric) fields allow to stabilize orientational structure. In thin layers of LC, the proper surface treatment can also provide the given orientation (e.g., planar or homeotropic, see Chapter 2). Liquid crystal with a stabilized orientational structure can be considered a conventional Newtonian fluid with shear viscosity determined by a field direction [1] or by a surfaceinduced direction. Such rheological behavior has to be taken into account at viscometric studies of liquid crystals. It will be described in detail in Chapter 5.A number of interesting flow-induced phenomena in smectic A and C phases are out of scope of this book. A reader can find description of such effects in Oswald and Pieranski [2] and in original papers [3,4]. We also do not consider rheological behavior of polymeric liquid crystals, lyotropic liquid crystals, and active liquid crystals. The last two classes of LC materials are of interest for understanding very complicated phenomena existing in living nature. In particular, active liquid crystals show unusual rheological properties that demand a special consideration [5][6][7].

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Section: Couette and Poiseuille Flows In Isotropic Liquids And Liquidmentioning

confidence: 86%

“…These parameters are defined as [16] Re ¼ rlv h ð3:2Þ So some common rheological effects, shear thinning, for example, were established for them too.…”

Section: Couette and Poiseuille Flows In Isotropic Liquids And Liquidmentioning

confidence: 99%

Section: Hydrodynamic Instabilities In Couette and Poiseuille Steady mentioning

confidence: 99%

Section: Hydrodynamic Instabilities In Couette and Poiseuille Steady mentioning

confidence: 99%

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Flows of Anisotropic Liquids

2009

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“…1). Applying rectilinear shear different types of stationary patterns were found for homeotropic initial alignment.…”

Section: Introductionmentioning

confidence: 95%

<title>Pattern formation in homeotropic nematic induced by mechanical rectilinear and elliptical oscillatory excitation</title>

et al. 1998

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A homeotropic nematic liquid crystal was exposed to low frequency oscillatory shear (Couette flow). In the presence of rectilinear shear a stationary roll pattern was found above a critical amplitude (Ar). In case of elliptical excitation a spatially nonuniform slow rotation of the director was observed, which lead to the propagation of the so called phase waves in two different systems: in a two-phase (nematic-isotropic) system and in a homeotropic nematic layer in the presence of a destabilizing external electric field. Phase waves also have been observed in the ultrasonic frequency range at much smaller shear amplitudes.

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