Observation of Forming Process of Bubble Domain Texture in Liquid Crystals

Nawa, Nobuhiko; Nakamura, Kenichi

doi:10.1143/jjap.17.219

Cited by 26 publications

(14 citation statements)

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“…11 The helical structure of cholesteric LCs (CLCs) does not readily accommodate many confinement geometries. When CLCs are confined in slit cells with the cell gap close to cholesteric pitch, bubble domain defects are often observed under thermal quenching, 12 external electric field, [13][14][15][16][17][18] or illuminations of focused laser beams. [19][20][21][22][23] By microscopically reconstructing the director fields, Smalyukh and coworkers showed that the bubble domain defects are made of either torons or baby Skyrmions (2D Skyrmions).…”

Section: Introductionmentioning

confidence: 99%

Cholesteric liquid crystals in rectangular microchannels: skyrmions and stripes

et al. 2016

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In this paper, we present experimental and numerical studies on the microstructures of a cholesteric liquid crystal (CLC) confined in rectangular micron-channels. By using a sequence of microfabrication techniques we fabricated the micro-sized channels with accurately controlled size, aspect ratio and homeotropic surface anchoring. Through optical microscopic studies we established a phase diagram for the liquid crystal defect textures as a function of the channel depth and width. For the channel width larger than ∼2 times the cholesteric pitch p, the LC molecules are oriented primarily vertical to the channel when the channel depth is below 0.75p, form bubble domain defects when the channel depth is around 0.75p, and form stripe textures when the cell depth is above the cholesteric pitch p. In addition, the bubble domain size and the stripe texture periodicity are found to grow with the increase of the channel width. For the channel width smaller than ∼2p and the channel depth between 0.6p to 1.1p, no textures can be observed in the channels. Numerical simulations based on a director tensor relaxation approach yield detailed molecular director fields, and show that the bubble domain defects are baby-skyrmions and that the stripes are the first type of cholesteric fingerprints. A comparison with previous experiments and numerical simulations indicates that the size of the microchannels also influences what type of soliton-like topological textures form in the CLCs confined in the channels.

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Section: Introductionmentioning

confidence: 99%

Cholesteric liquid crystals in rectangular microchannels: skyrmions and stripes

et al. 2016

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“…We have found that some of the studied laser-generated structures can also be obtained spontaneously when cooling the samples from the isotropic phase (although less reliably and without the control of spatial locations) and after applying low-frequency (10 Hz) electric fields to induce hydrodynamic instability. These localized structures, along with torons and hopfions, are several members of the large family of so-called cholesteric bubbles that were typically studied when occurring spontaneously, but not well understood in past experimental works [20,[34][35][36][37][38][39][40][41][42][43][44]. We note that the study of axially symmetric cholesteric configurations reported here is not exhaustive.…”

Section: Nested Axially Symmetric Structures Of Multiple Torons Anmentioning

confidence: 86%

“…We note that the study of axially symmetric cholesteric configurations reported here is not exhaustive. In fact, several other configurations might have been already identified in prior literature [20,[23][24][25][26][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48] that we have not explored so far using our 3D imaging experiments and different types of generation (laser realignment, low-frequency electric field, temperature quench with and without temperature gradients). In addition, in future work, studies of mutually linked multi-toron and multihopfion configurations that also belong to this family will be reported [51].…”

Section: Nested Axially Symmetric Structures Of Multiple Torons Anmentioning

confidence: 99%

Two-dimensional skyrmions and other solitonic structures in confinement-frustrated chiral nematics

et al. 2014

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We explore spatially localized solitonic configurations of a director field, generated using optical realignment and laser-induced heating, in frustrated chiral nematic liquid crystals confined between substrates with perpendicular surface anchoring. We demonstrate that, in addition to recently studied torons and Hopf-fibration solitonic structures (hopfions), one can generate a host of other axially symmetric stable and metastable director field configurations where local twist is matched to the surface boundary conditions through introduction of point defects and loops of singular and nonsingular disclinations. The experimentally demonstrated structures include the so-called "baby-skyrmions" in the form of double twist cylinders oriented perpendicular to the confining substrates where their double twist field configuration is matched to the perpendicular boundary conditions by loops of twist disclinations. We also generate complex textures with arbitrarily large skyrmion numbers. A simple back-of-the-envelope theoretical analysis based on free energy considerations and the nonpolar nature of chiral nematics provides insights into the long-term stability and diversity of these inter-related solitonic field configurations, including different types of torons, cholestric-finger loops, two-dimensional skyrmions, and more complex structures comprised of torons, hopfions, and various disclination loops that are experimentally observed in a confinement-frustrated chiral nematic system.

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“…in CLC systems effectively, it becomes feasible to create stable/metastable structures with 3D inhomogeneous configuration of the LC director field. One example of such structures that can be interesting and promising from the point of view of practical application in optics is the so‐called cholesteric “bubbles” or bubble domain (BD) texture . This texture is usually observed for d / P in the vicinity of 1 and represents a self‐assembled single layer of uniformly sized bubbles embedded in the medium with uniform homeotropic orientation.…”

Section: Diffraction Structures In Clc Materials Induced By Electric mentioning

confidence: 99%

Cholesteric Liquid Crystal Materials for Tunable Diffractive Optics

Ryabchun

Bobrovsky

2018

Advanced Optical Materials

196

106

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refractive, diffraction and optical fiber components. In particular, diffraction grating (DG) is one of the key elements for the design and creation of modern optoelectronic devices. One of the most prominent materials for the creation of DGs is liquid crystals. The main feature of these systems is that liquid crystals combine properties such as optical anisotropy inherent for crystals and molecular mobility. High sensitivity to an external field, in particular to an electric field, makes liquid crystals very useful for the creation of DGs with tunable properties. The combination of these properties enables easy control of optical characteristics of such systems and opens wide perspectives for the design of new materials for diffractive optics.Among the different types of liquid crystalline (LC) phases, cholesteric liquid crystal (CLC) phase possesses intrinsic periodicity in the form of the helical supramolecular structure (Figure 1). With the realization of definite alignment conditions, this periodicity has been exploited for generation of DGs. [8,9] Another remarkable feature of the cholesteric mesophase is selective light reflection with the reflection wavelength determined by the simple Equation (1) where n is the average refractive index, and P is the helix pitch. The specific value of helix pitch depends on the chemical structure of the molecules forming the cholesteric phase and concentration of chiral moieties. One of the easiest ways to obtain the cholesteric mesophase is by doping the nematic matrix with chiral components (Figure 1). Variation of structure of chiral molecules by external stimuli leading, for examples, to the photoisomerization, is effectively used for fine tuning of the helix pitch. [10][11][12][13][14][15][16][17] In addition, the application of an electric field also provides a convenient opportunity to change optical properties of the CLC phase. [18][19][20][21] These unique properties enable to design a great variety of optical elements and devices based on CLC layers, films, or cells. Among them it is necessary to mention the media for photo-optical data recording, [22][23][24][25] electrically switchable mirrors, [26,27] optically controllable linearpolarization rotators, [28] coatings with controllable friction and adhesion, [29] materials for display technology, [23,30] secure Modern optics and photonics constantly require break-through materials and designs in order to achieve miniature, lightweight, highly tunable, and effective optical devices. One of the basic optical components is the diffraction grating (DG), widely used for the dispersion of light, beam steering, etc. This review gathers research efforts on diffractive optical elements based on cholesteric liquid crystal (CLC) materials with a supramolecular helical architecture. All main types and fabrication approaches of periodic diffractive structures from CLCs are classified and described. Key optical properties of DGs, their advantages and drawbacks are considered. Special attention is paid on the tunability of DG...

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Observation of Forming Process of Bubble Domain Texture in Liquid Crystals

Cited by 26 publications

References 0 publications

Cholesteric liquid crystals in rectangular microchannels: skyrmions and stripes

Cholesteric liquid crystals in rectangular microchannels: skyrmions and stripes

Two-dimensional skyrmions and other solitonic structures in confinement-frustrated chiral nematics

Cholesteric Liquid Crystal Materials for Tunable Diffractive Optics

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