Sensitivity of Cholesteric Films to Ultraviolet Exposure

Adams, James E.; Haas, W.

doi:10.1149/1.2407900

Cited by 15 publications

(2 citation statements)

References 6 publications

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“…In 1974, Haas et al prepared CLC mixtures based on chlorostilbenes and cholesteryl oleyl carbonate and demonstrated a light-induced CLC to isotropic (CLC / I) transition. 82,83 These mixtures of nematic chlorostilbenes with cholesteryl oleyl carbonate were focal conic at room temperature, whereas after exposure to UV light the exposed regions became isotropic and transparent. Mioskowski et al developed a photoresponsive CLC mixture based on the photodecarbonylation of chiral ketones.…”

Section: A Photoresponsive Non-liquid Crystalline Materialsmentioning

confidence: 99%

Dynamic color in stimuli-responsive cholesteric liquid crystals

2010

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is the acronym used around the English-speaking world to aid children in the memorization of the traditional colors of the rainbow (red, orange, yellow, green, blue, indigo, and violet). Color surrounds us and the ability to change color by external stimuli (heat, force, light exposure, magnetic or electric field) continues to be leveraged for many present day applications. This review focuses on the state of the art in the use of cholesteric liquid crystals (CLCs) as color changing optical materials. After a brief summary of thermal and electrically induced color changes, the bulk of the article describes recent efforts in photoresponsive CLCs, materials in which light is used to control the color output.

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Section: A Photoresponsive Non-liquid Crystalline Materialsmentioning

confidence: 99%

Dynamic color in stimuli-responsive cholesteric liquid crystals

2010

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“…Adams and Haas investigated the pitch change in cholesteryl nonanoate/cholesteryl iodide by ultraviolet (UV) irradiation. [37,38] Upon irradiation, photodecomposition of cholesteryl iodide reduces its ratio in the mixed system, thus resulting in a cholesteric pitch change. In studies concerning the effect of a small amount of a photochromic dopant, Sackmann reported a pitch change induced by reversible photochemical reactions such as photoisomerization of azobenzene and stilbene in a mixture of cholesteryl chloride and cholesteryl nonanoate.…”

Section: Photochemical Control Of Cholesteric Pitchmentioning

confidence: 99%

Cholesteric Liquid Crystals for Color Information Technology

2001

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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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Sensitivity of Cholesteric Films to Ultraviolet Exposure

Abstract: not Available.

Cited by 15 publications

References 6 publications

Dynamic color in stimuli-responsive cholesteric liquid crystals

Dynamic color in stimuli-responsive cholesteric liquid crystals

Cholesteric Liquid Crystals for Color Information Technology

Thermography Using Liquid Crystals

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