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Takaki Yamamoto, Masaki Sano
We recently reported the experimental realization of a chiral artificial microswimmer exhibiting helical self-propulsion [T. Yamamoto and M. Sano, Soft Matter 13, 3328 (2017)1744-683X10.1039/C7SM00337D]. In the experiment, cholesteric liquid crystal (CLC) droplets dispersed in surfactant solutions swam spontaneously, driven by the Marangoni flow, in helical paths whose handedness is determined by the chirality of the component molecules of CLC. To study the mechanism of the emergence of the helical self-propelled motion, we propose a phenomenological model of the self-propelled helical motion of the CLC droplets...
January 2018: Physical Review. E
Tatsuya Shirai, Min Shuai, Keita Nakamura, Akihiro Yamaguchi, Yumiko Naka, Takeo Sasaki, Noel A Clark, Khoa V Le
We investigated the pitches of cholesteric liquid crystals prepared by mixing disodium cromoglycate (DSCG) in water with 5 different water-soluble chiral additives. The measurements are based on the Grandjean-Cano wedge cell method. Overall, the twisting effect is weak, and the shortest pitch of 2.9 ± 0.2 μm is obtained using trans-4-hydroxy-l-proline, by which the cholesteric sample is iridescent at certain viewing angles. Freeze-fracture transmission electron microscopy (FFTEM) was also performed for the first time on both the nematic and cholesteric phases, revealing that stacked chromonic aggregates are very long, up to a few hundred nm, which explains why cholesteric chromonic liquid crystals hardly have pitches in the visible wavelength region...
February 14, 2018: Soft Matter
Yuan Shen, Yan-Chao Xu, Ya-Hao Ge, Rong-Guo Jiang, Xiao-Zhong Wang, Sen-Sen Li, Lu-Jian Chen
We present a convenient photoalignment approach to fabricate rewritable fingerprint textures with designed geometrical patterns based on methyl red doped cholesteric liquid crystals (MDCLCs). MDCLC systems with/without nanoparticles of polyhedral oligomeric silsesquioxanes (POSS) were employed to realize two types of sophisticated binary patterns, respectively. Based on the understanding of involved mechanisms related to boundary conditions and middle-layer theory, we demonstrated the precise manipulation of fingerprint patterns by varying the fingerprint grating vectors in different domains...
January 22, 2018: Optics Express
Ziqian He, Haiwei Chen, Yun-Han Lee, Shin-Tson Wu
We report a new electrically tunable color filter to actively adjust the correlated color temperature of white light-emitting diodes. With four passive cholesteric films and an active polarization rotator, both circular polarizations of the incident light are utilized to generate complementary blue and yellow colors. The blue/yellow ratio can be tuned by the applied voltage of the polarization rotator. In experiment, the tunable color filter offers a reasonably wide tuning range (1900 K and 2400 K), which resembles the Planckian locus...
January 22, 2018: Optics Express
Yuelan Lu, Yue Yang, Yan Wang, Lei Wang, Ji Ma, Lingli Zhang, Weimin Sun, Yongjun Liu
The lasing behaviors of dye-doped cholesteric liquid crystal (DDCLC) microshells fabricated with silica-glass-microsphere coated DDCLCs were examined. Lasing characteristics were studied in a carrier medium with different refractive indices. The lasing in spherical cholesteric liquid crystals (CLCs) was attributed to two mechanisms, photonic band-gap (PBG) lasing and whispering-gallery modes (WGMs), which can independently exist by varying the chiral agent concentration and pumping energy. It was also found that DDCLC microshells can function as highly sensitive thermal sensors, with a temperature sensitivity of 0...
February 5, 2018: Optics Express
Jun Yoshioka, Fumito Araoka
When heat flux is applied to a chiral liquid crystal, unidirectional rotation is induced around the flux axis, as first discovered by Otto Lehmann in 1900. In recent years, this heat-flux-induced phenomenon has been studied mostly in droplets of cholesteric liquid crystals undergoing phase transition from the isotropic to cholesteric phase, i.e., in the coexistence region, which occurs over a very narrow temperature range. Here, we report that the heat-flux-induced rotation can be stabilised by the use of a dispersion system, in which the cholesteric droplets are dispersed in a viscous and poorly miscible isotropic solvent...
January 30, 2018: Nature Communications
Greta Babakhanova, Zeinab Parsouzi, Sathyanarayana Paladugu, Hao Wang, Yu A Nastishin, Sergij V Shiyanovskii, Samuel Sprunt, Oleg D Lavrentovich
We present a comprehensive set of measurements of optical, dielectric, diamagnetic, elastic, and viscous properties in the nematic (N) phase formed by a liquid crystalline dimer. The studied dimer, 1,7-bis-4-(4'-cyanobiphenyl) heptane (CB7CB), is composed of two rigid rodlike cyanobiphenyl segments connected by a flexible aliphatic link with seven methyl groups. CB7CB and other nematic dimers are of interest due to their tendency to adopt bent configurations and to form two states possessing a modulated nematic director structure, namely, the twist-bend nematic, N_{TB}, and the oblique helicoidal cholesteric, Ch_{OH}, which occurs when the achiral dimer is doped with a chiral additive and exposed to an external electric or magnetic field...
December 2017: Physical Review. E
Julio C Hernández, J Adrián Reyes
We analyzed the optical band gaps for axially propagating electromagnetic waves throughout a metallic doped cholesteric elastomer. The composed medium is made of metallic nanospheres (silver) randomly dispersed in a cholesteric elastomer liquid crystal whose dielectric properties can be represented by a resonant effective uniaxial tensor. We found that the band gap properties of the periodic system greatly depend on the volume fraction of nanoparticles in the cholesteric elastomer. In particular, we observed a displacement of the reflection band for quite small fraction volumes whereas for larger values of this fraction there appears a secondary band in the higher frequency region...
December 2017: Physical Review. E
Guilhem Poy, Felix Bunel, Patrick Oswald
We present a numerical method to compute defect-free textures inside cholesteric domains of arbitrary shape. This method has two interesting properties, namely a robust and fast quadratic convergence to a local minimum of the Frank free energy, thanks to a trust region strategy. We apply this algorithm to study the texture of cholesteric droplets in coexistence with their isotropic liquid in two cases: when the anchoring is planar and when it is tilted. In the first case, we show how to determine the anchoring energy at the cholesteric-isotropic interface from a study of the optical properties of droplets of different sizes oriented with an electric field...
July 2017: Physical Review. E
Sajedeh Afghah, Jonathan V Selinger
Cholesteric liquid crystals experience geometric frustration when they are confined between surfaces with anchoring conditions that are incompatible with the cholesteric twist. Because of this frustration, they develop complex topological defect structures, which may be helicoids or skyrmions. We develop a theory for these structures, which extends previous theoretical research by deriving exact solutions for helicoids with the assumption of constant azimuth, calculating numerical solutions for helicoids and skyrmions with varying azimuth, and interpreting the results in terms of competition between terms in the free energy...
July 2017: Physical Review. E
Setarehalsadat Changizrezaei, Colin Denniston
In this paper, we demonstrate the presence of a photonic band gap for a diamond lattice structure made of particles with normal anchoring inside a cholesteric liquid crystal. As is typical for liquid crystals (LCs), there is considerable contrast between the dielectric constant parallel ε_{∥} and perpendicular ε_{⊥} to the director, with ε_{∥}/ε_{⊥}∼4 here. It is shown that the size of the photonic band gap is directly related to the size of colloidal particles and the contrast between the dielectric constant in the particles and the extreme values of ε in the LC medium (one needs either ε in the particle much smaller than ε_{⊥} or much bigger than ε_{∥})...
September 2017: Physical Review. E
Lina Liang, Jun Fu, Liyan Qiu
pH-responsive polymersomes have emerged as promising nanocarriers for antitumor drugs to realize their fast release and action in weak acidic microenvironment of tumor cells. Herein, however, we designed a remarkably pH-responsive polymersome self-assembled from amphiphilic benzimidazole-based polyphosphazenes via the incorporation of cholesteryl hemisuccinate (CholHS), a type of cholesteric molecule, into the polymersome bilayers to inhibit the drug release during blood circulation. Actually, unwanted premature drug leakage before arriving at acidic tumor site has become a serious problem for polymersomes encapsulating water-soluble drugs, especially when the drug-loading is at a high level, thus limiting the therapeutic efficacy...
January 17, 2018: ACS Applied Materials & Interfaces
Peng Chen, Ling-Ling Ma, Wei Duan, Ji Chen, Shi-Jun Ge, Zhi-Han Zhu, Ming-Jie Tang, Ran Xu, Wei Gao, Tao Li, Wei Hu, Yan-Qing Lu
Cholesteric liquid crystal (CLC) chiral superstructures exhibit unique features; that is, polychromatic and spin-determined phase modulation. Here, a concept for digitalized chiral superstructures is proposed, which further enables the arbitrary manipulation of reflective geometric phase and may significantly upgrade existing optical apparatus. By encoding a specifically designed binary pattern, an innovative CLC optical vortex (OV) processor is demonstrated. Up to 25 different OVs are extracted with equal efficiency over a wavelength range of 116 nm...
January 15, 2018: Advanced Materials
Monali Moirangthem, Albertus P H J Schenning
A blue reflective photonic polymer coating which can be patterned in full color, from blue to red, by printing with an aqueous calcium nitrate solution has been fabricated. Color change in the cholesteric liquid crystalline polymer network over the entire visible spectrum is obtained by the use of non-reactive mesogen. The pattern in the coating is hidden in the blue color dry state and appears on exposure to water or by exhaling breath onto it due to different degrees of swelling of the polymer network. The degree of swelling depends on the printed amount of calcium which acts as a crosslinker...
January 9, 2018: ACS Applied Materials & Interfaces
Hao Wang, Hari Bisoyi, Ling Wang, Augustine Urbas, Timothy Bunning, Quan Li
We report the synthesis of a novel halogen bonded light-driven axially chiral molecular switch. The photoactive halogen bonded chiral switch is able to induce a self-organized, tunable helical superstructure, i.e., cholesteric liquid crystal (CLC), when doped into an achiral liquid crystal host. The halogen bonded switch as a chiral dopant is found to possess high helical twisting power (HTP) and shows a large change of its HTP upon photoisomeriza-tion. This light-driven dynamic modulation of structure has enabled reversible selective reflection color tuning across the entire visible spectrum...
December 29, 2017: Angewandte Chemie
Wanshu Zhang, Lanying Zhang, Le Zhou, Jingxuan Zhang, Fasheng Li, Kexuan Li, Huai Yang
Novel mesogenic [60]fullerenes have been synthesized and doped into cholesteric liquid crystals (CLCs) to achieve a dual-mechanism laser protection system that is effective for both pulsed and broadband cw lasers, simultaneously. It was found that this system integrated a good OPL response, broadband protection range, and high practicability with great potentials in flexible and even wearable protection devices.
December 18, 2017: Chemical Communications: Chem Comm
Maxime M C Tortora, Jonathan P K Doye
We detail the application of bounding volume hierarchies to accelerate second-virial evaluations for arbitrary complex particles interacting through hard and soft finite-range potentials. This procedure, based on the construction of neighbour lists through the combined use of recursive atom-decomposition techniques and binary overlap search schemes, is shown to scale sub-logarithmically with particle resolution in the case of molecular systems with high aspect ratios. Its implementation within an efficient numerical and theoretical framework based on classical density functional theory enables us to investigate the cholesteric self-assembly of a wide range of experimentally relevant particle models...
December 14, 2017: Journal of Chemical Physics
Giorgio Cinacchi, Alberta Ferrarini, Achille Giacometti, Hima Bindu Kolli
Recent numerical simulations of hard helical particle systems unveiled the existence of a novel chiral nematic phase, termed screw-like, characterised by the helical organization of the particle C2 symmetry axes round the nematic director with periodicity equal to the particle pitch. This phase forms at high density and can follow a less dense uniform nematic phase, with relative occurrence of the two phases depending on the helix morphology. Since these numerical simulations were conducted under three-dimensional periodic boundary conditions, two questions could remain open...
December 14, 2017: Journal of Chemical Physics
Nicholas A Yaraghi, David Kisailus
Nature assembles weak organic and inorganic constituents into sophisticated hierarchical structures, forming structural composites that demonstrate impressive combinations of strength and toughness. Two such composites are the nacre structure forming the inner layer of many mollusk shells, whose brick-and-mortar architecture has been the gold standard for biomimetic composites, and the cuticle forming the arthropod exoskeleton, whose helicoidal fiber-reinforced architecture has only recently attracted interest for structural biomimetics...
December 13, 2017: Annual Review of Physical Chemistry
Liang Wu, Huai Sun
The understanding of cholesteric liquid crystals at a molecular level is challenging. Limited insights are available to bridge between molecular structures and macroscopic chiral organization. In the present study, we introduce a novel coarse-grained (CG) molecular model, which is represented by flexible chain particles with helical interactions (FCh), to study the liquid crystalline phase behavior of cholesteric molecules such as double strand DNA and α-helix polypeptides using molecular dynamics (MD) simulations...
December 6, 2017: Soft Matter
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