Dynamics of jumpwise temperature pitch variations in planar cholesteric layers for a finite strength of surface anchoring

Belyakov, V. A.; Stewart, I. W.; Osipov, M. A.

doi:10.1134/1.1787080

Cited by 24 publications

(37 citation statements)

References 16 publications

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“…As the temperature is changed, so-called pitch jumps occur which are easily observable as changes in the selective reflection wavelength. There have been several reports of thermal hysteresis in the pitch jumps [2][3][4], as well as theoretical treatments that relate the hysteresis to parameters including surface anchoring and cell thickness [5][6][7][8].…”

Section: Introductionmentioning

confidence: 98%

An experimental investigation of discrete changes in pitch in a thin, planar chiral nematic device

2006

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The phenomenon whereby sudden changes in helicoidal pitch occur in thin chiral nematic devices with strong surface anchoring has been studied experimentally. This has been done with the aim of examining the underlying process in the context of existing theory. Thin devices (,2.5 mm thick) containing two commercially available chiral nematic liquid crystals were employed in the study. The samples were chosen for their dependence of pitch on temperature; one exhibits a very slow increase in pitch with increasing temperature (95.6% of the Merck material BL131 in BL130), while the second shows the more common rapid reduction in pitch with increasing temperature (the Merck mixture TM1001). High resolution reflection spectra were obtained for the devices and a numerical fitting algorithm, based on the Berreman 464 matrix technique, provided accurate information on changes in the pitch, refractive indices, device thickness and changes in the surface director across the pitch jump region. We demonstrate that changes in refractive index and device thickness are negligible in analysis of the reflection spectra across the pitch jumps. We further show that the pitch changes discontinuously at the pitch jump, with no variation in its value as the process occurs. We find evidence that the surface directors also change by less than 10u during this process in a manner analogous to coiling or uncoiling a constrained spring. This mechanism differs somewhat from others proposed in the literature.

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Section: Introductionmentioning

confidence: 98%

An experimental investigation of discrete changes in pitch in a thin, planar chiral nematic device

2006

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“…It should also be possible to extend the present analysis to more complicate forms of the surface energy [8,14,18,[1][2][3]. The physically correct form of this energy term has been disputed for some time and it would be very interesting to see if this type of uniqueness proof could be applied to systems with other forms of surface energy.…”

Section: Remarksmentioning

confidence: 98%

Uniqueness in the Freedericksz transition with weak anchoring

Costa

Grinfeld

Mottram

et al. 2009

Journal of Differential Equations

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In this paper we consider a boundary value problem for a quasilinear pendulum equation with nonlinear boundary conditions that arises in a classical liquid crystals setup, the Freedericksz transition, which is the simplest opto-electronic switch, the result of competition between reorienting effects of an applied electric field and the anchoring to the bounding surfaces. A change of variables transforms the problem into the equation x = −f(x) for ∈ (−T, T), with boundary conditions x = ± T f(x) at = ∓T, for a convex nonlinearity f. By analyzing an associated inviscid Burgers' equation, we prove uniqueness of monotone solutions in the original nonlinear boundary value problem. This result has been for many years conjectured in the liquid crystals literature, e. g. in E. G. Virga, Variational Theories for Liquid Crystals,Chapman and Hall, London, 1994 and in I. W. Stewart, The Static and Dynamic Continuum Theory of Liquid Crystals: A Mathematical Introduction, Taylor and Francis, London, 2003

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“…The physical motivation for the B form of surface energy is largely driven by pitch 'jumps' in cholesteric liquid crystals where the twist of the director is dominant and is related to the twist elastic constant K 2 [3][4][5]. By considering simple series expansions, it can be shown that the RP and B energies almost coincide when the actual surface twist angle is close to the easy direction / Ã .…”

Section: Introductionmentioning

confidence: 95%

“…if the director at the surface coincides with the easy direction. Recently, however, Belyakov et al [3][4][5] proposed an alternative form for a weak anchoring energy density that is particularly relevant to twist geometries. In our notation, this alternative version may be written as…”

Section: Introductionmentioning

confidence: 98%

Weak Anchoring Effects in Nematic Liquid Crystals

McKay

Kidney

Stewart

2007

Molecular Crystals and Liquid Crystals

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We consider a twisted nematic liquid crystal confined by two parallel boundary plates. The nematic is subject to an in-plane magnetic field applied in a direction parallel to the plates. At the lower plate the director is strongly anchored so that the director twist is fixed. On the upper surface we introduce an easy direction for the director. Although the director prefers to align with the easy direction, the actual twist exhibited at the upper surface may differ from the easy direction twist. This is due to the competition between elastic, magnetic and anchoring effects. We examine and compare two surface energies that model the weak anchoring at the upper plate. For both energies, equilibrium twist profiles for the director within the sample have been obtained by minimizing the total free energy for the system.

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Dynamics of jumpwise temperature pitch variations in planar cholesteric layers for a finite strength of surface anchoring

Cited by 24 publications

References 16 publications

An experimental investigation of discrete changes in pitch in a thin, planar chiral nematic device

An experimental investigation of discrete changes in pitch in a thin, planar chiral nematic device

Uniqueness in the Freedericksz transition with weak anchoring

Weak Anchoring Effects in Nematic Liquid Crystals

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