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Yuna Kim, Michel Frigoli, Nicolas Vanthuyne, Nobuyuki Tamaoki
The first photoresponsive cholesteric liquid crystal comprising a photoisomerizable helical naphthopyran derivative dopant and a nematic liquid crystal is reported. An unprecedented helical twisting power switching ratio of over 90% allowed us to demonstrate multi-cycle rotational motion of micro-objects by UV light irradiation.
December 5, 2016: Chemical Communications: Chem Comm
A Kuhnhold, T Schilling
We present a Monte Carlo simulation study of helical Yukawa rods as a model for chiral liquid crystal mesogens. To simulate the cholesteric phase, we introduce a new simulation method that uses soft walls and self-determined boundary conditions. We observe that the isotropic-nematic phase transition is shifted to lower volume fractions with decreasing salt concentration as well as with increasing internal pitch of the rods. For particular sets of interaction parameters, the sense of the cholesteric pitch inverts, i...
November 21, 2016: Journal of Chemical Physics
Mi-Yun Jeong, Keumcheol Kwak
In this study, we achieved active fine laser tuning in a broad spectral range with dye-doped cholesteric liquid crystal wedge-type cells through temperature control. The spatial pitch gradient of each position of the wedge cell at room temperature was almost maintained after developing a temperature gradient. To achieve the maximum tuning range, the chiral dopant concentration, thickness, thickness gradient, and temperature gradient on the wedge cell should be matched properly. In order to understand the laser tuning mechanism for temperature change, we studied the temperature dependence of optical properties of the photonic bandgap of cholesteric liquid crystals...
November 20, 2016: Applied Optics
Susete N Fernandes, Pedro L Almeida, Nuno Monge, Luis E Aguirre, Dennys Reis, Cristiano L P de Oliveira, António M F Neto, Pawel Pieranski, Maria H Godinho
A new photonic structure is produced from cellulose nanocrystal iridescent films reflecting both right and left circularly polarized light. Micrometer-scale planar gaps perpendicular to the films' cross-section between two different left-handed films' cholesteric domains are impregnated with a nematic liquid crystal. This photonic feature is reversibly tuned by the application of an electric field or a temperature variation.
November 9, 2016: Advanced Materials
Gonzague Agez, Chloé Bayon, Michel Mitov
: Beetles from the genus Chrysina show vivid reflections from bright green to metallic silver-gold as a consequence of the cholesteric liquid crystal organization of chitin molecules. Particularly, the cuticle of Chrysina gloriosa exhibits green and silver stripes. By combining confocal microscopy and spectrophotometry, scanning electron microscopy and numerical simulations, the relationship between the reflectance and the structural parameters for both stripes at the micro- and nanoscales are established...
November 14, 2016: Acta Biomaterialia
S G Skuridin, F V Vereshchagin, V I Salyanov, D P Chulkov, O N Kompanets, Yu M Yevdokimov
The current notion of the organization of molecules in a cholesteric phase is fairly well substantiated in the case of low-molecular-weight compounds. However, this question is open to discussion in the case of double-stranded nucleic acids. In this work, an attempt to compare the well-known data on the structure of cholesteric phases formed by double-stranded DNA molecules and the results of experimental modeling obtained by the authors has been undertaken. The comparison brings leads to assumption regarding the high probability of the existence of both short-range (positional) and long-range (orientational) order in the arrangement of double-stranded DNA molecules in the liquid crystalline phase...
September 2016: Molekuliarnaia Biologiia
Yo Inoue, Hiroshi Moritake
We investigated the possibility of practical applications using cholesteric liquid crystals (ChLCs) with Helfrich deformation, which causes the undulation of the helical structure. Usually, the Helfrich deformation is very unstable and can be obtained only in the transient state for a short time (< 10 s) under continuous field application. Here, we found that a ChLC polymerized with spatial pattern distribution exhibited high durability of the Helfrich deformation. Furthermore, we revealed molecular alignment of the Helfrich deformation by scanning electron microscope...
October 3, 2016: Optics Express
Yong Li, Dan Luo, Rui Chen
We demonstrate random lasing from a scattering system formed by a cholesteric liquid crystal dispersed in glycerol. Strong scattering of light is produced from the interference between the cholesteric liquid crystal microsphere and glycerol and leads to random lasing. The optical properties of random lasing, such as intensity, threshold, and the temperature effect on lasing emission are demonstrated. The random laser is distinguished from the band-edge laser generated within the cholesteric liquid crystal microspheres by analyzing the positions of the photonic band-edge of the cholesteric liquid crystal and the photoluminescence of the doped laser dye...
November 1, 2016: Applied Optics
Jie Xiang, Andrii Varanytsia, Fred Minkowski, Daniel A Paterson, John M D Storey, Corrie T Imrie, Oleg D Lavrentovich, Peter Palffy-Muhoray
A cholesteric liquid crystal (CLC) formed by chiral molecules represents a self-assembled one-dimensionally periodic helical structure with pitch [Formula: see text] in the submicrometer and micrometer range. Because of the spatial periodicity of the dielectric permittivity, a CLC doped with a fluorescent dye and pumped optically is capable of mirrorless lasing. An attractive feature of a CLC laser is that the pitch [Formula: see text] and thus the wavelength of lasing [Formula: see text] can be tuned, for example, by chemical composition...
November 2, 2016: Proceedings of the National Academy of Sciences of the United States of America
O F Aguilar Gutierrez, Alejandro D Rey
Dilute isotropic collagen solutions are usually flow processed into monodomain chiral nematic thin films for obtaining highly ordered materials by a multistep process that starts with complex inhomogeneous flow kinematics. Here we present rigorous theory and simulation of the initial precursors during flow steps in cholesteric collagen film formation. We first extract the molecular shape parameter and rotational diffusivity from previously reported simple shear data of dilute collagen solutions, where the former leads the reactive parameter (tumbling function) which determines the net effect of vorticity and strain rate on the average orientation and where the latter establishes the intensity of strain required for flow-birefringence, both crucial quantities for controlled film formation flow...
October 31, 2016: Langmuir: the ACS Journal of Surfaces and Colloids
Oliver Wiese, Davide Marenduzzo, Oliver Henrich
We explore the rheology and flow-induced morphological changes of cholesteric liquid crystal patterns subject to Poiseuille flow within a slab geometry, and under different anchoring conditions at the wall. Our focus is particularly on the behaviour of "Cholesteric Fingers of the first kind" and of Blue Phase II. Depending on the applied pressure gradient, we observe a number of dynamic regimes with different rheological properties. Our results provide the first insight into the flow response of cholesteric phases with fully two- or three-dimensional director field patterns and normal and planar degenerate anchoring conditions as commonly realised in experiments...
November 16, 2016: Soft Matter
Alexandre Darmon, Michael Benzaquen, Simon Čopar, Olivier Dauchot, Teresa Lopez-Leon
We investigate experimentally and numerically the defect configurations emerging when a cholesteric liquid crystal is confined to a spherical shell. We uncover a rich scenario of defect configurations, some of them non-existent in nematic shells, where new types of defects are stabilized by the helical ordering of the liquid crystal. In contrast to nematic shells, here defects are not simple singular points or lines, but have a large structured core. Specifically, we observe five different types of cholesteric shells...
October 21, 2016: Soft Matter
Sangho Cho, Yunfeng Li, Minseok Seo, Eugenia Kumacheva
We report composite stimulus-responsive cholesteric catalytically active microgels derived from filamentous supramolecular building blocks: cellulose nanocrystals (CNCs). The variation in the microgel dimensions and pitch in response to the change in ambient conditions was governed by the polymer component. The cholesteric morphology of the microgels resulted from the self-organization of CNCs in spherical confinement. The microgels exhibited excellent structural integrity and functioned as microreactors in catalytic hydrolysis reactions and in the synthesis of metal nanoparticles...
October 13, 2016: Angewandte Chemie
Emre Bukusoglu, Xiaoguang Wang, Ye Zhou, José A Martínez-González, Mohammad Rahimi, Qi Wang, Juan J de Pablo, Nicholas L Abbott
We report on the internal configurations of aqueous dispersions of droplets of cholesteric liquid crystals (LCs; 5-50 μm-in-diameter; comprised of 4-cyano-4'-pentylbiphenyl and 4-(1-methylheptyloxycarbonyl)phenyl-4-hexyloxybenzoate) and their influence on the positioning of surface-adsorbed colloids (0.2 or 1 μm-in-diameter polystyrene (PS)). When N = 2D/P was less than 4, where D is the droplet diameter and P is the cholesteric pitch, the droplets adopted a twisted bipolar structure (TBS) and colloids were observed to assume positions at either the poles or equator of the droplets...
October 5, 2016: Soft Matter
Alain Dequidt, Guilhem Poy, Patrick Oswald
We propose a general method to calculate the drift velocity of cholesteric textures subjected to a temperature gradient when the backflow effects are negligible. The textures may be Translationally Invariant Configurations (TICs) or localized structures such as cholesteric droplets or cholesteric fingers. For the TICs and for the droplets, the drift is rotational while for the fingers, the drift is translational. We show that for the TICs, the drift is only due to the thermomechanical coupling terms of Leslie (classical term) and of Akopyan and Zel'dovich (which are additional texture-dependent terms)...
September 13, 2016: Soft Matter
Dae-Yoon Kim, Changwoon Nah, Shin-Woong Kang, Seung Hee Lee, Kyung Min Lee, Timothy J White, Kwang-Un Jeong
The preparation of materials exhibiting structural colors have been intensively studied in biomimetic science and technology. Utilizing a newly synthesized cholesteric liquid crystal (CLC) monomer (abbreviated as BP1CRM), we have prepared CLC films. Photoinitiated copolymerization of this monomer with a common achiral liquid crystalline monomer produced free-standing films with homogenous and nanoscale pitch distributions. Employing the thermal sensitivity of the CLC monomer, chirophotonic crystal reflectors were prepared exhibiting a range of colors...
September 19, 2016: ACS Nano
Karla G Gutierrez-Cuevas, Ling Wang, Zhi-Gang Zheng, Hari K Bisoyi, Guoqiang Li, Loon-Seng Tan, Richard A Vaia, Quan Li
Adding colloidal nanoparticles into liquid-crystal media has become a promising pathway either to enhance or to introduce novel properties for improved device performance. Here we designed and synthesized new colloidal hybrid silica nanoparticles passivated with a mesogenic monolayer on the surface to facilitate their organo-solubility and compatibility in a liquid-crystal host. The resulting nanoparticles were identified by (1) H NMR spectroscopy, TEM, TGA, and UV/Vis techniques, and the hybrid nanoparticles were doped into a dual-frequency cholesteric liquid-crystal host to appraise both their compatibility with the host and the effect of the doping concentration on their electro-optical properties...
October 10, 2016: Angewandte Chemie
Alexander Ryabchun, Ivan Raguzin, Joachim Stumpe, Valery Shibaev, Alexey Bobrovsky
The past two decades witnessed tremendous progress in the field of creation of different types of responsive materials. Cholesteric polymer networks present a very promising class of smart materials due to the combination of the unique optical properties of cholesteric mesophase and high mechanical properties of polymer networks. In the present work we demonstrate the possibility of fast and reversible photocontrol of the optical properties of cholesteric polymer networks. Several cholesteric photopolymerizable mixtures are prepared, and porous cholesteric network films with different helix pitches are produced by polymerization of these mixtures...
October 12, 2016: ACS Applied Materials & Interfaces
Hyun-Gyu Lee, Sundas Munir, Soo-Young Park
By utilizing a microfluidics approach, we prepared uniformly sized cholesteric liquid crystal (CLC) droplets from MLC-2132 doped with a chiral dopant (S)-4-cyano-4'-(2-methylbutyl)biphenyl (CB15). We studied the helical structures and reflecting color patterns of high- and low-dopant CLC droplets coated with poly(vinyl alcohol) (PVA) and sodium dodecyl sulfate (SDS). One central large spot with reflecting color in the CLC droplets (initially coated with PVA for planar anchoring) changed to many small spots with the same reflecting color (chicken-skin pattern) when an SDS aqueous solution was introduced to increase the homeotropic anchoring power...
October 5, 2016: ACS Applied Materials & Interfaces
Bradley Worth, Kyung Min Lee, Vincent P Tondiglia, Joshua Myers, Shin Mou, Timothy J White
We report on the formulation and electrical control of the position and bandwidth of reflective bandpass filters prepared from cholesteric liquid crystal (CLC) in the infrared (3-5 μm). These filters are prepared from alignment cells employing infrared transparent electrodes and substrates. The optical nature of the electrodes is shown to strongly influence the resulting transmission of the bandpass filters outside of the spectral reflection.
September 1, 2016: Applied Optics
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