Selective Reflection of Cholesteric Liquid Crystals

Elser, Wolfgang; Ennulat, Reinhard D.

doi:10.1016/b978-0-12-025002-8.50009-9

Cited by 40 publications

(16 citation statements)

References 252 publications

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“…[1][2][3][4][5][6][7] CLCs are characterised by a macroscopically ordered chiral structure where the molecules are organised in nematic layers, whose director orientation varies periodically along the direction perpendicular to the planes. The rotation of the director produces a righthanded or left-handed helix.…”

Section: Induced Cholesteric Solutions Of Highly Soluble Bissalicylalmentioning

confidence: 99%

Induced cholesteric solutions of highly soluble bis-salicylaldiminate Cu(II) metallomesogens and their rheological behaviour

et al. 2015

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Copper(II) complexes containing chiral centres and functionalised with citronellyl end groups were synthesised.\ud Isomerisation of citronellyl double bond was exploited to decrease the melting temperature of the complexes and\ud improve their solubility in organic media. The chiral metallomesogens were successfully used to produce induced\ud cholesteric solutions in commercial nematic liquid crystals also in high concentrations. Transparent and coloured\ud thin films were easily obtained showing good reflective properties across the visible spectrum. The rheological\ud behaviour of the nematic and the cholesteric phases was investigated. The nematic system showed the characteristics\ud of a tumbling phase with a very peculiar transient behaviour. The cholesteric samples also showed a very\ud unusual, flow-history-dependent transient behaviour. The viscosity trend presumably indicates a flow-induced\ud orientation of the cholesteric superstructure, thus opening the way to the possibility of tuning the yield stress level\ud of the material. The results support the potentiality of these compounds for applications in light reflecting\ud technology

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Section: Induced Cholesteric Solutions Of Highly Soluble Bissalicylalmentioning

confidence: 99%

Induced cholesteric solutions of highly soluble bis-salicylaldiminate Cu(II) metallomesogens and their rheological behaviour

et al. 2015

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“…Equation (3) assumes that the head conduction along the fin is negligible and the fin temperature is uniform across its thickness. Integration of this equation with the initial condition T= To at t = 0 gives, (4) where tG is the time necessary for the fin element in consideration to reach the temperature TG.…”

Section: Engineering and Aerodynamic Researchmentioning

confidence: 99%

“…The use of cholesteric liquid crystals for thermography was reviewed some years ago by Elser and Ennulat [4], and more recently in the commercial literature of Hallcrest [5]. Amongst the substances with the largest temperature coefficient are cholesteryl oleyl carbonate [6] and S-cholesteryl esters Figure 1.…”

Section: Introductionmentioning

confidence: 99%

Thermography Using Liquid Crystals

Gleeson¹

1998

Handbook of Liquid Crystals Set

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The dramatic variation of liquid crystalline properties with respect to temperature has resulted in the widespread use of cholesteric (chiral nematic) liquid crystals for thermography. The property that has been exploited most in liquid crystal thermography is the critical temperature dependence of the selective reflection from cholesteric liquid crystals, though other temperature dependent properties of mesophases have been utilized (e.g. the birefringence of nematic systems and selective reflection from other chiral phases). The helicoidal structure of cholesteric materials results in the selective reflection of visible light within a band of wavelengths of width Ahcentered at a wavelength ho, such that:Here, p is the pitch of the helical structure, An is the birefringence of the medium and ii is the average refractive index, (no + n J 2 .The temperature range over which the cholesteric material selectively reflects visible light is known as the colorplay of the material. The temperature dependence of the selective reflection from a cholesteric material is a consequence of the temperature variation of the pitch of the system, defined by the twist elastic constants. A critical divergence of the selective reflection occurs if a cholesteric material cools when an underlying SmA phase is approached. This happens because the twist deformation is not allowed within a SmA phase, and the twist elastic constants (and therefore pitch) show pretransitional divergence. The pitch of the system increases rapidly as the temperature reduces towards the SmA phase transition temperature, typically resulting in the reflection of red light at lower temperatures. In cholesteric materials without a SmA phase, the critical divergence of the selective reflection is less pronounced. Indeed, in some materials the selective reflection is at a constant wavelength over the entire temperature range. Thus materials that exhibit a low lying SmA phase possess the most useful thermal properties for most thermography applications, though temperature insensitive materials have found application as shear sensitive systems (see Sec. 3.3). At higher temperatures within the cholesteric phase (above any pretransitiona1 region) the pitch may either increase or decrease with increasing temperature, due

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“…Further, we have investigated the effect of an artificial cholesterol derivative, cholesterol benzoate (BENZO, Scheme 1), on membrane stability. Since BENZO can form a cholesterol liquid crystal (LC) state, when in the presence of other natural cholesterol derivatives such as Cholesterol oleyl carbonate (CHOL OC) and Cholesterol pelargonate (CHOL PA) (Scheme 2) [6,7] we aimed to investigate its effect on membrane dynamics. In particular, our choice was motivated by the similarities in structure between DOPC lipid and CHOL PA, CHOL OC.…”

Section: Introductionmentioning

confidence: 99%

Thermo‐induced Vesicular Dynamics of Membranes Containing Cholesterol Derivatives

Yoda¹,

Vestergaard²,

Hamada³

et al. 2012

Lipids

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Membrane structural organization is an intrinsic property of a cell membrane. Any changes in lipid composition, and/or any stimuli that affect molecular packing induce structural re-organization. It membrane dynamics provide a means by which changes in structure organization can be determined, upon a change in the membrane internal or external environment. Here, we report on the effect of thermo-stress on membranes containing cholesterol liquid crystal (LC) compounds cholesterol benzoate (BENZO) and oxidized cholesterols. We have (1) revealed that lipid vesicles containing this artificial cholesterol derivative (BENZO) is thermo-responsive, and that this thermo-sensitivity is significantly similar to naturally oxy-cholesterols (2) elucidated the mechanism behind the membrane perturbation. Using Langmuir monolayer experiments, we have demonstrated that membrane perturbation was due to an increase in the molecular surface area, (3) discussed the similarities between cholesterol benzoate in the cholesterol LC state and in lipid bilayer membranes. Last, (4) drawing from previously reported findings, our new data on membrane dynamics, and the discussion above, we propose that artificial cholesterol derivatives such as BENZO, open new possibilities for controlled and tailored design using model membrane systems. Examples could include the development of membrane technology and provide a trigger for progress in thermo-tropical liquid crystal engineering.

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Selective Reflection of Cholesteric Liquid Crystals

Cited by 40 publications

References 252 publications

Induced cholesteric solutions of highly soluble bis-salicylaldiminate Cu(II) metallomesogens and their rheological behaviour

Induced cholesteric solutions of highly soluble bis-salicylaldiminate Cu(II) metallomesogens and their rheological behaviour

Thermography Using Liquid Crystals

Thermo‐induced Vesicular Dynamics of Membranes Containing Cholesterol Derivatives

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