Cholesteric pitch-transitions induced by a magnetic field in a sample containing incomplete number of pitches

Lelidis, I.; Barbero, Giovanni; Scarfone, Antonio Maria

doi:10.2478/s11534-012-0050-y

Cited by 7 publications

(6 citation statements)

References 21 publications

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“…More recently, Scarfone et al [20] generalize the problem of [19] to consider an in-plane magnetic field tilted at some angle with respect to fixed parallel twist directions on the substrates. The analysis of Lelidis et al [21] allows for an incomplete number of half twists in the liquid crystal layer by imposing strong homogeneous anchoring with non-parallel director twists on the two confining plates.…”

Section: Introductionmentioning

confidence: 99%

Unwinding of a cholesteric liquid crystal and bidirectional surface anchoring

McKay

2013

J Eng Math

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We examine the influence of bidirectional anchoring on the unwinding of a planar cholesteric liquid crystal induced by the application of a magnetic field. We consider a liquid crystal layer confined between two plates with the helical axis perpendicular to the substrates. We fixed the director twist on one boundary and allow for bidirectional anchoring on the other by introducing a high-order surface potential. By minimizing the total free energy for the system, we investigate the untwisting of the cholesteric helix as the liquid crystal attempts to align with the magnetic field. The transitions between metastable states occur as a series of pitchjumps as the helix expels quarter or half-turn twists, depending on the relative sizes of the strength of the surface potential and the bidirectional anchoring. We show that secondary easy axis directions can play a significant role in the unwinding of the cholesteric in its transition towards a nematic, especially when the surface anchoring strength is large.

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Section: Introductionmentioning

confidence: 99%

Unwinding of a cholesteric liquid crystal and bidirectional surface anchoring

McKay

2013

J Eng Math

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“…This work is a natural continuation of the previous studies [28,29], where a cell of CLC with finite thickness with a strong anchoring at the limiting surfaces is perturbed by an external field. In that case it also has been shown how the system expels twists one by one in a sequence that accumulates toward the critical value, signifying the CLC → NLC final transition.…”

Section: Discussionmentioning

confidence: 72%

“…In Refs. [28,29], we have generalized previous studies, relevant to the CLC → NLC transition induced by a magnetic field, by assuming strong anchoring on the limiting surfaces of the cell. In this framework, it has been shown that, as the external field increases in its strength, the system expels one twist at a time until a certain critical value is reached, beyond which the system passes from the cholesteric to the nematic phase.…”

Section: Introductionmentioning

confidence: 99%

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Cholesteric-nematic transition in an asymmetric strong-weak anchoring cell

Barbero

Scarfone

2013

Phys. Rev. E

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We discuss the cholesteric-nematic transition induced by an external field in a cell in the shape of a slab of finite thickness whose anchoring energy is infinitely strong on one surface and negligible on the other. The case where the surface orientations of the cholesteric director are parallel in the ground state is considered. In a sample of thickness ℓ, multiple of the natural periodicity of the system Λ, the number of complete twists in the cholesteric liquid crystal is reduced by increasing the strength of the external distorting field. The sequence of the field values for expelling complete twists accumulate as the strength of the field approaches a critical value. Beyond this critical value the system assumes an unwinding configuration going toward a uniform structure, corresponding to nematic phase. Generalization of the results to the weak-weak anchoring cell case is also discussed. In our analysis the anisotropic part of the surface energy is assumed or very large or very small with respect to the total energy per unit surface due to the bulk distortion induced by the magnetic field.

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“…The instability mechanism underlying the pitch transitions has been discussed by Kiselev and Sluckin in [10]. Recently, Scarfone et al [11,12] have shown that in the limit of infinite thickness the analysis presented in [3,4] yields the results reported in [1]. Experimental observations of CLC pitch transitions have been reported in [13][14][15][16][17][18].…”

Section: Introductionmentioning

confidence: 99%

Cholesteric pitch transitions induced by mechanical strain

2013

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We investigate thickness and surface anchoring strength influence on pitch transitions in a planar cholesteric liquid crystal layer. The cholesteric-nematic transition is also investigated. We assume planar boundary conditions, with strong anchoring strength at one interface and weak anchoring strength at the other. The surface anchoring energy we consider to describe the deviation of the surface twist angle from the easy axis induced by a bulk deformation is a parabolic potential or Rapini and Papoular periodic potential, respectively. We show that under strain, all pitch transitions take place at a critical thickness that is equal to the quarter of the natural cholesteric pitch. The latter result does not depend on the anchoring strength, the particular surface potential, or material properties. The twist angle on the limiting surface characterized by weak anchoring varies with strain either by slipping and or in a discontinuous manner according to the thickness of the sample. The position of the bifurcation point depends only on the ratio of the extrapolation length over the layer thickness, but its value is model dependent. Multistability and multiplicity of the transition are discussed.

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Cholesteric pitch-transitions induced by a magnetic field in a sample containing incomplete number of pitches

Cited by 7 publications

References 21 publications

Unwinding of a cholesteric liquid crystal and bidirectional surface anchoring

Unwinding of a cholesteric liquid crystal and bidirectional surface anchoring

Cholesteric-nematic transition in an asymmetric strong-weak anchoring cell

Cholesteric pitch transitions induced by mechanical strain

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