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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
Richard M Parker, Bruno Frka-Petesic, Giulia Guidetti, Gen Kamita, Gioele Consani, Chris Abell, Silvia Vignolini
Complex hierarchical architectures are ubiquitous in nature. By designing and controlling the interaction between elementary building blocks, nature is able to optimize a large variety of materials with multiple functionalities. Such control is, however, extremely challenging in man-made materials, due to the difficulties in controlling their interaction at different length scales simultaneously. Here, hierarchical cholesteric architectures are obtained by the self-assembly of cellulose nanocrystals within shrinking, micron-sized aqueous droplets...
September 27, 2016: ACS Nano
Yunfeng Li, Jeffrey Jun-Yan Suen, Elisabeth Prince, Egor M Larin, Anna Klinkova, Héloïse Thérien-Aubin, Shoujun Zhu, Bai Yang, Amr S Helmy, Oleg D Lavrentovich, Eugenia Kumacheva
The organization of nanoparticles in constrained geometries is an area of fundamental and practical importance. Spherical confinement of nanocolloids leads to new modes of packing, self-assembly, phase separation and relaxation of colloidal liquids; however, it remains an unexplored area of research for colloidal liquid crystals. Here we report the organization of cholesteric liquid crystal formed by nanorods in spherical droplets. For cholesteric suspensions of cellulose nanocrystals, with progressive confinement, we observe phase separation into a micrometer-size isotropic droplet core and a cholesteric shell formed by concentric nanocrystal layers...
2016: Nature Communications
Matjaž Humar, Fumito Araoka, Hideo Takezoe, Igor Muševič
Dye doped photocurable cholesteric liquid crystal was used to produce solid Bragg onion omnidirectional lasers. The lasers were produced by dispersing and polymerizing chiral nematic LC with parallel surface anchoring of LC molecules at the interface, extracted and transferred into another medium. Lasing characteristics were studied in carrier medium with different refractive index. The lasing in spherical cholesteric liquid crystal was attributed to two mechanisms, photonic bandedge lasing and lasing of whispering-gallery modes...
August 22, 2016: Optics Express
Sahil Sandesh Gandhi, Min Su Kim, Jeoung-Yeon Hwang, Liang-Chy Chien
An electro-optical (EO) memory device is presented, which is based on a 3D nanostructured polymer scaffold of the amorphous blue phase III (BPIII) of cholesteric liquid crystals (LCs), which can impart optical isotropy, optical activity, and sub-millisecond EO response of BPIII to conventional nematic LCs. This functional scaffold also enables the first experimental observation of the long debated structure of BPIII.
August 24, 2016: Advanced Materials
W L Leaw, C R Mamat, S Triwahyono, A A Jalil, N Bidin
A liquid crystal physical gel was prepared by the self-assembly of cholesteryl stearate in a nematic liquid crystal, 4-cyano-4'-pentylbiphenyl. The electro-optical properties were tuned by varying the gelator concentration and the gelation conditions. Polarized optical microscopy revealed that cholesteric cholesteryl stearate induced chiral nematic phase in 4-cyano-4'-pentylbiphenyl during the gelation process. As a result, a plate-like gel structure consisting of spherical micropores was formed, as observed by scanning electron microscopy...
December 1, 2016: Journal of Colloid and Interface Science
Jordi Ignés-Mullol, Guilhem Poy, Patrick Oswald
Suspended droplets of cholesteric (chiral nematic) liquid crystals spontaneously rotate in the presence of a heat flux due to a temperature gradient, a phenomenon known as the Lehmann effect. So far, it is not clear whether this effect is due to the chirality of the phase and the molecules or only to the chirality of the director field. Here, we report the continuous rotation in a temperature gradient of nematic droplets of a lyotropic chromonic liquid crystal featuring a twisted bipolar configuration. The achiral nature of the molecular components leads to a random handedness of the spontaneous twist, resulting in the coexistence of droplets rotating in the two senses, with speeds proportional to the temperature gradient and inversely proportional to the droplet radius...
July 29, 2016: Physical Review Letters
Thomas Machon, Gareth P Alexander
We give the global homotopy classification of nematic textures for a general domain with weak anchoring boundary conditions and arbitrary defect set in terms of twisted cohomology, and give an explicit computation for the case of knotted and linked defects in [Formula: see text], showing that the distinct homotopy classes have a 1-1 correspondence with the first homology group of the branched double cover, branched over the disclination loops. We show further that the subset of those classes corresponding to elements of order 2 in this group has representatives that are planar and characterize the obstruction for other classes in terms of merons...
July 2016: Proceedings. Mathematical, Physical, and Engineering Sciences
Alexandre Darmon, Michael Benzaquen, David Seč, Simon Čopar, Olivier Dauchot, Teresa Lopez-Leon
Liquid crystals, when confined to a spherical shell, offer fascinating possibilities for producing artificial mesoscopic atoms, which could then self-assemble into materials structured at a nanoscale, such as photonic crystals or metamaterials. The spherical curvature of the shell imposes topological constraints in the molecular ordering of the liquid crystal, resulting in the formation of defects. Controlling the number of defects, that is, the shell valency, and their positions, is a key success factor for the realization of those materials...
August 23, 2016: Proceedings of the National Academy of Sciences of the United States of America
Cornelia Rosu, Sreelatha Balamurugan, Rafael Cueto, Amitava Roy, Paul S Russo
When a particle is introduced into a liquid crystal (LC), it distorts the LC director field, leading to new arrangements of the particles. This phenomenon is ordinarily studied using >100 nm particles and ∼2 nm mesogens. Usually the particle surface and mesogens are chemically distinct, which adds an enthalpic effect, even though the more interesting interactions are entropic. To raise the structures to the visible regime, while minimizing chemical differences between the particle surface and mesogen, silica particles coated with an α-helical polypeptide have been prepared and dispersed in lyotropic polypeptide LCs...
July 28, 2016: Journal of Physical Chemistry. B
Yubing Guo, Sajedeh Afghah, Jie Xiang, Oleg D Lavrentovich, Robin L B Selinger, Qi-Huo Wei
Correction for 'Cholesteric liquid crystals in rectangular microchannels: skyrmions and stripes' by Yubing Guo et al., Soft Matter, 2016, DOI: 10.1039/c6sm01190j.
August 14, 2016: Soft Matter
Gyu Jin Choi, Hye Min Jung, Seung Hee Lee, Jin Seog Gwag
In this paper, we propose an infrared light shutter device using cholesteric liquid crystals. The pitch of the device corresponds to the wavelengths of the infrared region with a strong thermal effect. This device is intended for use as a smart window to maintain an optimal indoor temperature by controlling the infrared radiation coming from the sun. The proposed cholesteric device switches between the planar state and the isotropic state by controlling the temperature using an electrically heated transparent electrode made of indium tin oxide...
June 1, 2016: Applied Optics
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