Characterization of Molecular Role in Pitch Determination in Liquid Crystal Mixtures

Adams, James E.; Haas, W.

doi:10.1080/15421407108083221

Cited by 48 publications

(4 citation statements)

References 8 publications

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“…These numerical results are consistent with the experimental results. 2,8,[11][12][13] The pitch strongly depends on the chiral interaction parameter x between a polymer and a liquid crystal.…”

Section: A Cholesteric Pitch Depending On Concentration and Temperaturementioning

confidence: 99%

“…[7][8][9][10] The pitch and the physical properties of cholesterics can be controlled by mixing cholesteric liquid crystals and polymer chains, or photo reactive molecules. 2,[11][12][13] It has been shown both experimentally [14][15][16][17] and theoretically [18][19][20][21][22][23][24][25] that in mixtures of a polymer and a liquid crystal (so-called polymer dispersed liquid crystals: PDLCs), phase separations between an isotropic and a nematic or a smectic phase appears below the nematic-isotropic phase transition (NIT) temperature of the pure liquid crystal. 2 For strong anisotropic (attractive) interactions between polymers and liquid crystals, it has been recognized that a smectic phase can be induced in a nematic liquid crystal mixture.…”

Section: Introductionmentioning

confidence: 99%

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Theory of polymer-dispersed cholesteric liquid crystals

Matsuyama

2013

The Journal of Chemical Physics

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A mean field theory is presented to describe cholesteric phases in mixtures of a polymer and a cholesteric liquid crystal. Taking into account an anisotropic coupling between a polymer and a liquid crystal, we examine the helical pitch, twist elastic constant, and phase separations. Analytical expressions of the helical pitch of a cholesteric phase and the twist elastic constant are derived as a function of the orientational order parameters of a polymer and a liquid crystal and two intermolecular interaction parameters. We also find isotropic-cholesteric, cholesteric-cholesteric phase separations, and polymer-induced cholesteric phase on the temperature-concentration plane. We demonstrate that an anisotropic coupling between a polymer and a liquid crystal can stabilize a cholesteric phase in the mixtures. Our theory can also apply to mixtures of a nematic liquid crystal and a chiral dopant. We discuss the helical twisting power, which depends on temperature, concentration, and orientational order parameters. It is shown that our theory can qualitatively explain experimental observations.

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Section: A Cholesteric Pitch Depending On Concentration and Temperaturementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Theory of polymer-dispersed cholesteric liquid crystals

Matsuyama

2013

The Journal of Chemical Physics

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“…In a chiral nematic phase with a chiral dopant, helical pitch ( p ) is given by p − 1 = β c where β is helical twisting power (HTP), c is a molar fraction of the chiral dopant, and the signs “+” and “–” of p and β represent right- and left-handedness of helical mesostructures, respectively. In a chiral nematic system with multiple chiral components, an additive law is often applied: p − 1 = ∑ i β i c i where β i and c i denote the HTP and molar fraction of the i th component, respectively. − Azobenzenes with chirality can be used as dopants in LCs, of which HTP can be switched through the trans – cis isomerization of the azobenzene moieties. Photoinduced change in HTP has been applied to control reflection wavelength of chiral nematic LCs in planar alignment. ,− Furthermore, transparent–scattering transition has been achieved by using LCs containing both azobenzene and photoinert chiral dopants with the opposite signs of HTP to each other. − These compensated nematic LCs with p –1 = 0 show transparent states in homeotropic alignment, whereas photoisomerization leads to the change in HTPs of chiral azobenzenes and results in the transition to scattering states with chiral nematic mesostructure.…”

Section: Introductionmentioning

confidence: 99%

Sunlight-Driven Smart Windows with a Wide Temperature Range of Optical Switching Based on Chiral Nematic Liquid Crystals

Ube,

Yoshida,

Kurihara

et al. 2024

ACS Appl. Mater. Interfaces

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Photoresponsive liquid crystals are promising materials for sunlightdriven smart windows, which can automatically change their optical states in response to sunlight and control energy flow between the inside and outside of a building. Herein, liquid-crystalline systems are developed that show a transparent-scattering transition upon irradiation with sunlight in a wide temperature range. Push−pull azobenzenes with axial chirality have been newly developed as photochromic chiral dopants to allow changes in mesostructures of liquid crystals in response to sunlight. To realize optical switching, photochromic and photoinert chiral compounds with opposite handedness of helical twisting are doped in liquid crystals. This liquid crystalline sample with a compensated nematic phase is transparent in its initial state. Upon irradiation with sunlight, this sample transforms to a scattering state due to the formation of helical mesostructures along with photoisomerization of azobenzene moieties and the change in the helical twisting power. After the cease of irradiation, the sample reverts to the transparent state through thermal back isomerization of azobenzene moieties. This system significantly improves the operating temperature range of sunlightdriven smart windows based on liquid crystals: the transparent−scattering transition is observed at 4−42 °C. The present mechanism allows development of autonomous and wireless smart windows adaptable to various environments.

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“…The concentration of chiral compounds in nematic LC-1289 was taken 0.01-0.02 mole fraction. For practical use HTP values are also expressed in mass fractions.The cholesteric helix handedness (twisting sign) was determined according to Adams-Haas method[26]. For cases when the cholesteric helix handedness was notdetermined, HTP values are given as absolute values.…”

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confidence: 99%