Behavior of lattice parameter in cholesteric blue phases

Her, J.; Rao, B. B.; Ho, John T.

doi:10.1103/physreva.24.3272

Cited by 20 publications

(3 citation statements)

References 18 publications

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“…The previous papers reported that the temperature-dependent pitch length in BPI is the same as in the cholestric phase. [7,8] According to these papers, the helical pitch of our BP samples becomes longer when we increased the temperature. Then, we explore the Kossel lines and reflection spectra with two different temperatures in 14.93 wt% NL sample ( Figure 1).…”

Section: Resultsmentioning

confidence: 93%

“…[5,6] This means that the reflection colours of the BPs are dominated by two factors: the reflected lattice plane of these BPI platelets and the lattice constant. Referring to other previous studies, [4,7,8] the reflection colours of the cubic BPs may be different in the heating and cooling processes. When the LC was heated from the cholestric phase to BPI, the reflected lattice plane in BPI does not change, but the lattice constant does.…”

Section: Introductionmentioning

confidence: 85%

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Lattice structure in liquid-crystal blue phase with various chiral concentrations

Chen

Hsieh

2015

Liquid Crystals

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Lattice structures, including reflection lattice planes and lattice constant, of liquid-crystal blue phase I (BPI) are studied via the measurements on reflection spectrum and Kossel diagram as concentration of a chiral dopant is changed. Peaks of the reflection wavelength in BPI are mainly dominated by the lattice plane and the lattice constant, which are affected by the chiral concentration. In the chiral nematic state, as decreasing the chiral concentration the reflection peak will shift to a longer wavelength because the helical pitch linearly depends on the chiral concentration and becomes longer. However, this dependence of the chiral concentration and reflection wavelength is broken in the BPI. The reflection peak of BPI moves to a short wavelength when the chiral concentration is less due to the contraction of the lattice constant as well as helical pitch. Moreover, when the concentration of the chiral dopant increases over a certain value, a discontinuous shift in reflection peak occurs due to the production of the different lattice planes. It means that the relationship between the chiral concentration and the helical pitch in BPI is not the same as it in the chiral nematic phase and should be reconsidered.

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Section: Resultsmentioning

confidence: 93%

Section: Introductionmentioning

confidence: 85%

Lattice structure in liquid-crystal blue phase with various chiral concentrations

Chen

Hsieh

2015

Liquid Crystals

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“…In this last case, several techniques have recently been developed to study the unusual physical properties that result from the shift to colloidal scales. 4 The purpose of this Letter is to report the results of our measurements of the elastic shear modulus of BPI using the "oscillating cylinder" method. 5 The method is similar to the one used by Clark, Vohra, and Handschy 6 to measure the elastic modulus of BPI in a pure compound.…”

Section: Pawel Pieranski and Mathieu Joanicotmentioning

confidence: 99%

Elasticity of Blue Phase I of Cholesteric Liquid Crystals

1984

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Normal shear modes of axial symmetry were excited in poly crystalline samples of blue phase I. An average shear modulus, E t is determined from the frequencies of these modes. E is found to vary by nearly two orders of magnitude throughout the blue-phase temperature range. The authors report the first observation of faceted single crystals of blue phase I growing from the isotropic phase. These have enabled them to determine the blue phase I lattice constant.PACS numbers: 62.10, + s, 64.70.Ja, Cholesteric blue phases are those mysterious intermediate phases which appear in the ~ 0.5 °C temperature range between the cholesteric liquidcrystal phase of some short-pitch materials and the isotropic liquid phase. Although blue phases are the first example of thermotropic liquidcrystal phases (i.e.., obtained by varying the temperature) ever to be observed, it is only in the last few years that serious attempts have been made to understand them. 1 In the nematic liquid-crystal phase, rodiike (or disclike) molecules move freely in three directions but tend to align along a unique direction denoted by a unit vector, n, called the director. If the molecules are chiral, cholesteric liquidcrystal phases may occur where the director rotates with constant pitch, p, about an axis perpendicular ton. The nematic phase is, thus, the special case of a cholesteric phase with infinite pitch, A cholesteric reflects light the same wavelength as its pitch and polarized circularly in the same sense as its helical structure, e.g., a righthanded cholesteric reflects right circularly polarized light.Cholesteric liquid crystals undergo a first-order transition to the isotropic phase which, when the pitch is less than ~ 4000 A, is often, but not always, accompanied by the appearance of blue phases. Blue phases are optically active but isotropic and reflect several wavelengths all of which are circularly polarized in the same sense as the cholesteric phase. 2 These lengths can be indexed according to a cubic lattice. There are currently three kinds of blue phases: I, n, and the blue fog. When all three phases are present, blue phase I (BPI) is closest in temperature to the cholesteric phase and the fog is closest to the isotropic phase. In some cases, only one or two blue phases may occur. BPI is believed to be bcc (an/ lattice); BPII, simple cubic (aP lattice); and no lattice is associated with the fog. 1 Under the assumption that BPI is bcc, its lattice constant, a, turns out to be somewhat greater than the pitch, p 9 for a 2u rotation of the director in the cholesteric phase. The lattice constant decreases as one approaches the transition to BPII and is very nearly, but not exactly, commensurate with p at the transition BPI-BPII. 2 * 3 If one assumes that BPII is simple cubic, "a" is about p/2. Thus, blue-phase lattice constants are the same magnitude as those of colloidal crystals made of charged polymer particles dispersed in water. In this last case, several techniques have recently been developed to study the unusual physical prope...

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Lattice Parameters in Blue Phase Mixtures

Her

1984

Liquid Crystals and Ordered Fluids

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Behavior of lattice parameter in cholesteric blue phases

Cited by 20 publications

References 18 publications

Lattice structure in liquid-crystal blue phase with various chiral concentrations

Lattice structure in liquid-crystal blue phase with various chiral concentrations

Elasticity of Blue Phase I of Cholesteric Liquid Crystals

Lattice Parameters in Blue Phase Mixtures

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