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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
Chidambar Kulkarni, Daniele Di Nuzzo, E W Meijer, Stefan C J Meskers
The molecular organization in thermally annealed films of poly(9,9-bis((S)-3,7-dimethyloctyl)-2,7-fluorene-alt-benzothiadiazole) is investigated using polarized light. Measurement of linear polarization in transmission and reflection as function of layer thickness and orientation directly show a left handed cholesteric organization with a pitch length of 600 nm. Results are corroborated by measurements of circularly polarized reflection and generalized ellipsometry and are compared to calculations of the optical properties based on the Maugin-Oseen-DeVries model...
December 4, 2017: Journal of Physical Chemistry. B
Daniele Di Nuzzo, Chidambar Kulkarni, Baodan Zhao, Eilam Smolinsky, Francesco Tassinari, Stefan C J Meskers, Ron Naaman, E W Meijer, Richard H Friend
We demonstrate a facile route to obtain high and broad-band circular polarization of electro-luminescence in single layer polymer OLEDs. As light emitting material we use a donor-acceptor polyfluorene with enantiomerically pure chiral side-chains. We show that upon thermal annealing the polymer self assembles into a multi-domain cholesteric film. By varying the thickness of the polymer emitting layer, we achieve high levels of circular polarization of electro-luminescence (up to 40% excess of right-handed polarization), which are the highest reported for polymer OLEDs not using chiral dopants or alignment layers...
November 28, 2017: ACS Nano
Andrii Varanytsia, Gregor Posnjak, Urban Mur, Vinay Joshi, Kelsey Darrah, Igor Muševič, Simon Čopar, Liang-Chy Chien
Nowadays, complicated topological defects enable many experimental manipulations and configurational simulations of active soft matter for optical and photonic applications. Investigation of topological defects in soft anisotropic materials enables one to better understand three-dimensional orientation fields in cholesteric liquid crystals. Here, we describe optical properties of bistable bubble domain (BD) texture torons in a thin layer of cholesteric liquid crystal (CLC), frustrated by homeotropic anchoring conditions, and reliably switchable by a random process...
November 23, 2017: Scientific Reports
Meina Yu, Huai Yang, Deng-Ke Yang
When subjected to an AC electric field perpendicular to its layers, the cholesteric planar state may undergo a periodic layer undulation, known as the Helfrich deformation, which generates a color change of the reflected light. The Helfrich deformation of regular cholesteric liquid crystals is, however, unstable and easily taken over by the focal conic state, and thus the color tuning range is narrow. We demonstrated that the Helfrich deformation can be stabilized in a large electric field region by doping a bent dimer with an anomalously small bend elastic constant and dispersing a small amount of polymer network...
November 17, 2017: Soft Matter
Cheng-Kai Liu, Chian-Yu Chiu, Stephen M Morris, Min-Cheng Tsai, Chii-Chang Chen, Ko-Ting Cheng
A linear-polarization rotator based on the optically tunable pitch of chiral-azobenzene-doped liquid crystals (CAdLCs) has been investigated. It is shown that the orientation of linearly polarized (LP) light can be optically tuned using CAdLCs and that the transmitted light possesses a good degree of linear polarization (DoLP). Experimental and simulation (4 × 4 Berreman matrix) results show that the rotation angle is dependent on the pitch as well as the number of turns of the cholesteric LC helix. Some causes to affect the DoLP of the output LP lights during photoisomerization are also discussed...
November 13, 2017: Materials
Yali Lin, Yujie Yang, Yuwei Shan, Lingli Gong, Jingzhi Chen, Sensen Li, Lujian Chen
Cholesteric liquid crystals (CLCs) exhibit selective Bragg reflections of circularly polarized (CP) light owing to their spontaneous self-assembly abilities into periodic helical structures. Photonic cross-communication patterns could be generated toward potential security applications by spherical cholesteric liquid crystal (CLC) structures. To endow these optical patterns with tunability, we fabricated spherical CLC Bragg reflectors in the shape of microshells by glass-capillary microfluidics. Water-soluble magnetofluid with Fe₃O₄ nanoparticles incorporated in the inner aqueous core of CLC shells is responsible for the non-invasive transportable capability...
November 8, 2017: Nanomaterials
Jongyoon Kim, Hyungmin Kim, Seongil Kim, Suseok Choi, Wonbong Jang, Jinwuk Kim, Ji-Hoon Lee
We report a method of broadening the reflection bandwidth of polymer-stabilized cholesteric liquid crystal (PSCLC). The top substrate was consecutively coated with a polyimide (PI) and a reactive mesogen (RM) layer, while the bottom substrate was coated with only PI. We exposed the top substrate with the RM coating to UV light. The reflection bandwidth of the PSCLC samples where the top substrate was over-coated with RM was significantly broader than the samples where both substrates were coated with PI. In addition to the effect of the UV intensity gradient, the RM-coated top substrate has a chemical affinity to bulk RM, promoting formation of the pitch gradient and broadening the reflection bandwidth in the sample...
July 10, 2017: Applied Optics
Yong Li, Yanjun Liu, Dan Luo
We demonstrate an optical thermal sensor based on cholesteric film refilled with mixture of toluene and ethanol. The thermal response mechanism is mainly based on the thermal expansion effect induce by toluene, where the ethanol is used for refractive index adjustment to determine the initial refection band position of cholesteric film. The ethanol-toluene mixture was used to adjust the color tunability with the temperature in relation with the habits of people (blue as cold, green as safe and red as hot). A broad temperature range of 86 °C and highly sensitivity of 1...
October 16, 2017: Optics Express
Sahil Sandesh Gandhi, Liang-Chy Chien
The amorphous blue phase III of cholesteric liquid crystals, also known as the "blue fog," are among the rising stars in materials science that can potentially be used to develop next-generation displays with the ability to compete toe-to-toe with disruptive technologies like organic light-emitting diodes. The structure and properties of the practically unobservable blue phase III have eluded scientists for more than a century since it was discovered. This progress report reviews the developments in this field from both fundamental and applied research perspectives...
October 10, 2017: Advanced Materials
Peter Medle Rupnik, Darja Lisjak, Martin Čopič, Simon Čopar, Alenka Mertelj
One of the advantages of anisotropic soft materials is that their structures and, consequently, their properties can be controlled by moderate external fields. Whereas the control of materials with uniform orientational order is straightforward, manipulation of systems with complex orientational order is challenging. We show that a variety of structures of an interesting liquid material, which combine chiral orientational order with ferromagnetic one, can be controlled by a combination of small magnetic and electric fields...
October 2017: Science Advances
Weiguang Song, Dagang Liu, Nana Prempeh, Renjie Song
Sulfate cellulose nanocrystal (CNC) dispersions always present specific self-assembled cholesteric mesophases which is easily affected by the inherent properties of particle size, surface charge, and repulsion or affinity interaction, and external field force generated from ionic potential of added electrolytes, magnetic or electric field, and mechanical shearing or stretching. Aiming at understanding the liquid crystal orientation and fiber alignment under high-voltage electric field, randomly distributed, uniform-aligned, or core-sheath nanofibrous mats involving charged CNCs and PVA were electrospun; and among them, specific straight arrayed fine nanofibers with average diameter of 270 nm were manufactured by using a simple and versatile gap collector...
September 28, 2017: Biomacromolecules
Shinji Bono, Sayumi Sato, Yuka Tabe
We investigated the novel photo-induced dynamics of azobenzene-doped cholesteric (Ch) droplets coexisting with the isotropic (Iso) phase. When the hemispherical Ch droplets initially stuck to glass substrates were irradiated by UV-light, they were parted from the substrates due to the surface disordering caused by the photo-isomerization of azobenzene. Then, the spherical droplets floating in the Iso phase exhibited an unexpected motion - a continuous and unidirectional rotation along the light propagation direction...
September 27, 2017: Soft Matter
Mirosław Salamończyk, Nataša Vaupotič, Damian Pociecha, Cheng Wang, Chenhui Zhu, Ewa Gorecka
Periodic structures of phases with orientational order of molecules but homogenous electron density distribution: a short pitch cholesteric phase, blue phase and twist-bend nematic phase, were probed by resonant soft X-ray scattering (RSoXS) at the carbon K-edge. The theoretical model shows that in the case of a simple heliconical nematic structure, two resonant signals corresponding to the full and half pitch band should be present, while only the full pitch band is observed experimentally. This suggests that the twist-bend nematic phase has a complex structure with a double-helix built of two interlocked, shifted helices...
October 4, 2017: Soft Matter
Monali Moirangthem, Tom A P Engels, Jeffrey Murphy, Cees W M Bastiaansen, Albertus P H J Schenning
A photonic shape memory polymer film that shows large color response (∼155 nm) in a wide temperature range has been fabricated from a semi-interpenetrating network of a cholesteric polymer and poly(benzyl acrylate). The large color response is achieved by mechanical embossing of the photonic film above its broad glass transition temperature. The embossed film, as it recovers to its original shape on heating through the broad thermal transition, exhibits multiple structural colors ranging from blue to orange...
September 20, 2017: ACS Applied Materials & Interfaces
Shidong Dai, Nana Prempeh, Dagang Liu, Yimin Fan, Mingyue Gu, Yu Chang
With the increasing demand of environmental monitoring for toxic and odorous ammonia gas it is desired to develop specific green, cost-effective and in situ passive colorimetric alternatives to current complex instrumentations. In this work, we designed an ammonia gas sensor based on cholesteric liquid crystal films of copper(II)-doped cellulose nanocrystals (CNCCu(II)) whose structure, optical and sensing properties were investigated. The hybrid films using the low doping Cu(II) as a color-tuning agent inherited the chiral nematic signature and optical activity of CNCs, suggesting a strong chelation between copper ions and negatively charged CNCs...
October 15, 2017: Carbohydrate Polymers
F Berride, E Troche-Pesqueira, G Feio, E J Cabrita, T Sierra, A Navarro-Vázquez, M M Cid
Chromonic liquid crystals (CLC) are lyotropic phases formed by discotic mesogens in water. Simple chiral dopants such as amino acids have been reported to turn chromonic liquid crystals into their cholesteric counterparts. Here we report a chirality amplification effect in the nematic phase of a 9 wt% disodium cromoglycate (DSCG) lyotropic liquid crystal (LLC) upon doping with a water-soluble codeine derivative. The transition on cooling the isotropic to the nematic phase showed the presence of homochiral spindle-shaped droplets (tactoids)...
October 4, 2017: Soft Matter
Kyung Min Lee, Vincent P Tondiglia, Nicholas P Godman, Claire M Middleton, Timothy J White
We report on electrically-induced, large magnitude (>300 nm), and reversible tuning of the selective reflection in polymer stabilized cholesteric liquid crystals (PSCLCs) prepared from negative dielectric anisotropy nematic liquid crystal hosts. The electrically-induced blue shift in the selective reflection of the PSCLCs is distinguished from our prior reports of bandwidth broadening and red-shifting tuning of the selective reflection in PSCLCs. The dominant factor in delineating the electro-optic response of the PSCLCs detailed here are the preparation conditions...
September 13, 2017: Soft Matter
F Fadda, G Gonnella, D Marenduzzo, E Orlandini, A Tiribocchi
In this work we numerically study the switching dynamics of a 2D cholesteric emulsion droplet immersed in an isotropic fluid under an electric field, which is either uniform or rotating with constant speed. The overall dynamics depend strongly on the magnitude and on the direction (with respect to the cholesteric axis) of the applied field, on the anchoring of the director at the droplet surface and on the elasticity. If the surface anchoring is homeotropic and a uniform field is parallel to the cholesteric axis, the director undergoes deep elastic deformations and the droplet typically gets stuck into metastable states which are rich in topological defects...
August 14, 2017: Journal of Chemical Physics
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