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https://www.readbyqxmd.com/read/28635143/controlling-the-photonic-properties-of-cholesteric-cellulose-nanocrystal-films-with-magnets
#1
Bruno Frka-Petesic, Giulia Guidetti, Gen Kamita, Silvia Vignolini
The self-assembly of cellulose nanocrystals is a powerful method for the fabrication of biosourced photonic films with a chiral optical response. While various techniques have been exploited to tune the optical properties of such systems, the presence of external fields has yet to be reported to significantly modify their optical properties. In this work, by using small commercial magnets (≈ 0.5-1.2 T) the orientation of the cholesteric domains is enabled to tune in suspension as they assemble into films...
June 21, 2017: Advanced Materials
https://www.readbyqxmd.com/read/28630681/imaging-optical-scattering-of-butterfly-wing-scales-with-a-microscope
#2
Jinxin Fu, Beom-Jin Yoon, Jung Ok Park, Mohan Srinivasarao
A new optical method is proposed to investigate the reflectance of structurally coloured objects, such as Morpho butterfly wing scales and cholesteric liquid crystals. Using a reflected-light microscope and a digital single-lens reflex (DSLR) camera, we have successfully measured the two-dimensional reflection pattern of individual wing scales of Morpho butterflies. We demonstrate that this method enables us to measure the bidirectional reflectance distribution function (BRDF). The scattering image observed in the back focal plane of the objective is projected onto the camera sensor by inserting a Bertrand lens in the optical path of the microscope...
August 6, 2017: Interface Focus
https://www.readbyqxmd.com/read/28630672/circularly-polarized-reflection-from-the-scarab-beetle-chalcothea-smaragdina-light-scattering-by-a-dual-photonic-structure
#3
Luke T McDonald, Ewan D Finlayson, Bodo D Wilts, Pete Vukusic
Helicoidal architectures comprising various polysaccharides, such as chitin and cellulose, have been reported in biological systems. In some cases, these architectures exhibit stunning optical properties analogous to ordered cholesteric liquid crystal phases. In this work, we characterize the circularly polarized reflectance and optical scattering from the cuticle of the beetle Chalcothea smaragdina (Coleoptera: Scarabaeidae: Cetoniinae) using optical experiments, simulations and structural analysis. The selective reflection of left-handed circularly polarized light is attributed to a Bouligand-type helicoidal morphology within the beetle's exocuticle...
August 6, 2017: Interface Focus
https://www.readbyqxmd.com/read/28618483/heterogeneous-colloidal-particles-immersed-in-a-liquid-crystal
#4
Setarehalsadat Changizrezaei, Colin Denniston
In this paper, we explore anisotropic interactions between particles with heterogeneous boundary conditions inside both nematic and cholesteric liquid crystals. The results show that when particles are put at different distances and angles with respect to each other, new types of defect structures are produced, depending on the relative distances and directions. In a cholesteric liquid crystal, the value of the pitch affects the defect structures and induced forces. Moreover, it was observed that it is energetically favorable for the particles to remain in a plane parallel to the far-field director in a nematic liquid crystal, while for particles immersed in a cholesteric there are multiple energy minima not all located in the same plane...
May 2017: Physical Review. E
https://www.readbyqxmd.com/read/28590069/controllable-dynamic-zigzag-pattern-formation-in-a-soft-helical-superstructure
#5
Zhi-Gang Zheng, Rafael S Zola, Hari Krishna Bisoyi, Ling Wang, Yannian Li, Timothy J Bunning, Quan Li
Zigzag pattern formation is a common and important phenomenon in nature serving a multitude of purposes. For example, the zigzag-shaped edge of green leaves boosts the transportation and absorption of nutrients. However, the elucidation of this complicated shape formation is challenging in fluid mechanics and soft condensed matter systems. Herein, a dynamically reconfigurable zigzag pattern deformation of a soft helical superstructure is demonstrated in a photoresponsive self-organized cholesteric liquid crystal superstructure under the simultaneous influence of an applied electric field and light irradiation...
June 7, 2017: Advanced Materials
https://www.readbyqxmd.com/read/28589190/cholesteric-liquid-crystals-in-living-matter
#6
REVIEW
Michel Mitov
Liquid crystals play an important role in biology because the combination of order and mobility is a basic requirement for self-organisation and structure formation in living systems. Cholesteric liquid crystals are omnipresent in living matter under both in vivo and in vitro conditions and address the major types of molecules essential to life. In the animal and plant kingdoms, the cholesteric structure is a recurring design, suggesting a convergent evolution to an optimised left-handed helix. Herein, we review the recent advances in the cholesteric organisation of DNA, chromatin, chitin, cellulose, collagen, viruses, silk and cholesterol ester deposition in atherosclerosis...
June 14, 2017: Soft Matter
https://www.readbyqxmd.com/read/28571371/publisher-s-note-perturbative-density-functional-methods-for-cholesteric-liquid-crystals-j-chem-phys-146-184504-2017
#7
Maxime M C Tortora, Jonathan P K Doye
No abstract text is available yet for this article.
May 28, 2017: Journal of Chemical Physics
https://www.readbyqxmd.com/read/28530665/molecular-engineering-of-chiral-colloidal-liquid-crystals-using-dna-origami
#8
Mahsa Siavashpouri, Christian H Wachauf, Mark J Zakhary, Florian Praetorius, Hendrik Dietz, Zvonimir Dogic
Establishing precise control over the shape and the interactions of the microscopic building blocks is essential for design of macroscopic soft materials with novel structural, optical and mechanical properties. Here, we demonstrate robust assembly of DNA origami filaments into cholesteric liquid crystals, one-dimensional supramolecular twisted ribbons and two-dimensional colloidal membranes. The exquisite control afforded by the DNA origami technology establishes a quantitative relationship between the microscopic filament structure and the macroscopic cholesteric pitch...
May 22, 2017: Nature Materials
https://www.readbyqxmd.com/read/28497826/twisting-with-a-twist-supramolecular-helix-fluctuations-in-chiral-nematics
#9
Henricus Herman Wensink, Claudia Ferreiro-Córdova
Most theoretical descriptions of lyotropic cholesteric liquid crystals to date focus on homogeneous systems in which the rod concentration, as opposed to the rod orientation, is uniform. In this work, we build upon the Onsager-Straley theory for twisted nematics and study the effect of weak concentration gradients, generated by some external potential, on the cholesteric twist. We apply our theory to chiral nematics of nanohelices in which the supramolecular helix sense is known to spontaneously change sign upon variation of particle concentration, passing through a so-called compensation point at which the mesoscopic twist vanishes...
May 31, 2017: Soft Matter
https://www.readbyqxmd.com/read/28489951/direct-observation-of-changes-in-focal-conic-domains-of-cholesteric-films-induced-by-ultraviolet-irradiation
#10
Olga V Sinitsyna, Alexey Yu Bobrovsky, Georgy B Meshkov, Igor V Yaminsky, Valery P Shibaev
The helical supramolecular structure of cholesteric liquid crystalline (LC) films predetermines their outstanding optical properties and the unique nanostructure of their surface. The introduction of photochromic dopants in these films opens up an interesting possibility for creation of smart cholesteric materials with photocontrollable optical and photovariable surface properties. Using atomic force microscopy (AFM), we performed in situ measurements of the surface topography of cyclosiloxane LC cholesteric oligomer films during the cholesteric helix twisting caused by their preliminary ultraviolet (UV) irradiation...
May 23, 2017: Journal of Physical Chemistry. B
https://www.readbyqxmd.com/read/28429181/hydrodynamic-instabilities-in-active-cholesteric-liquid-crystals
#11
Carl A Whitfield, Tapan Chandra Adhyapak, Adriano Tiribocchi, Gareth P Alexander, Davide Marenduzzo, Sriram Ramaswamy
We describe the basic properties and consequences of introducing active stresses, with principal direction along the local director, in cholesteric liquid crystals. The helical ground state is found to be linearly unstable to extensile stresses, without threshold in the limit of infinite system size, whereas contractile stresses are hydrodynamically screened by the cholesteric elasticity to give a finite threshold. This is confirmed numerically and the non-linear consequences of instability, in both extensile and contractile cases, are studied...
April 2017: European Physical Journal. E, Soft Matter
https://www.readbyqxmd.com/read/28421224/chirality-induced-helical-self-propulsion-of-cholesteric-liquid-crystal-droplets
#12
Takaki Yamamoto, Masaki Sano
We report the first experimental realization of a chiral artificial microswimmer exhibiting helical motion without any external fields. We discovered that a cholesteric liquid crystal (CLC) droplet with a helical director field swims in a helical path driven by the Marangoni flow in an aqueous surfactant solution. We also showed that the handedness of the helical path is reversed when that of the CLC droplet is reversed by replacing the chiral dopant with the enantiomer. In contrast, nematic liquid crystal (NLC) droplets exhibited ballistic motions...
May 14, 2017: Soft Matter
https://www.readbyqxmd.com/read/28415267/dispersion-relation-for-electromagnetic-propagation-in-stochastic-dielectric-and-magnetic-helical-photonic-crystals
#13
Carlos G Avendaño, Arturo Reyes
We theoretically study the dispersion relation for axially propagating electromagnetic waves throughout a one-dimensional helical structure whose pitch and dielectric and magnetic properties are spatial random functions with specific statistical characteristics. In the system of coordinates rotating with the helix, by using a matrix formalism, we write the set of differential equations that governs the expected value of the electromagnetic field amplitudes and we obtain the corresponding dispersion relation...
March 2017: Physical Review. E
https://www.readbyqxmd.com/read/28402658/amplified-photon-upconversion-by-photonic-shell-of-cholesteric-liquid-crystals
#14
Ji-Hwan Kang, Shin-Hyun Kim, Alberto Fernandez-Nieves, Elsa Reichmanis
As an effective platform to exploit triplet-triplet-annihilation-based photon upconversion (TTA-UC), microcapsules composed of a fluidic UC core and photonic shell are microfluidically prepared using a triple emulsion as the template. The photonic shell consists of cholesteric liquid crystals (CLCs) with a periodic helical structure, exhibiting a photonic band gap. Combined with planar anchoring at the boundaries, the shell serves as a resonance cavity for TTA-UC emission and enables spectral tuning of the UC under low-power-density excitation...
April 17, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28401659/dynamic-orthogonal-switching-of-a-thermoresponsive-self-organized-helical-superstructure
#15
Lingli Zhang, Ling Wang, Uma S Hiremath, Hari Krishna Bisoyi, Geetha G Nair, Channabasaveshwar V Yelamaggad, Augustine M Urbas, Timothy J Bunning, Quan Li
Controllable manipulation of self-organized dynamic superstructures of functional molecular materials by external stimuli is an enabling enterprise. Herein, we have developed a thermally driven, self-organized helical superstructure, i.e., thermoresponsive cholesteric liquid crystal (CLC), by integrating a judiciously chosen thermoresponsive chiral molecular switch into an achiral liquid crystalline medium. The CLC in lying state, in both planar and twisted nematic cells, exhibits reversible in-plane orthogonal switching of its helical axis in response to the combined effect of temperature and electric field...
June 2017: Advanced Materials
https://www.readbyqxmd.com/read/28394559/dielectric-characterization-of-confined-water-in-chiral-cellulose-nanocrystal-films
#16
Bharath Natarajan, Caglar Emiroglu, Jan Obrzut, Douglas M Fox, Beatriz Pazmino, Jack F Douglas, Jeffrey W Gilman
A known deterrent to the large-scale development and use of cellulose nanocrystals (CNCs) in composite materials is their affinity for moisture, which has a profound effect on dispersion, wetting, interfacial adhesion, matrix crystallization, water uptake, and hydrothermal stability. To quantify and control the hydration and confinement of absorbed water in CNCs, we studied sulfated-CNCs neutralized with sodium cations and CNCs functionalized with less hydrophilic methyl(triphenyl)phosphonium cations. Films were cast from water suspensions at 20 °C under controlled humidity and drying rate, yielding CNC materials with distinguishably different dielectric properties and cholesteric structures...
April 14, 2017: ACS Applied Materials & Interfaces
https://www.readbyqxmd.com/read/28370481/structural-color-palettes-of-core-shell-photonic-ink-capsules-containing-cholesteric-liquid-crystals
#17
Sang Seok Lee, Hyeon Jin Seo, Yun Ho Kim, Shin-Hyun Kim
Photonic microcapsules with onion-like topology are microfluidically designed to have cholesteric liquid crystals with opposite handedness in their core and shell. The microcapsules exhibit structural colors caused by dual photonic bandgaps, resulting in a rich variety of color on the optical palette. Moreover, the microcapsules can switch the colors from either core or shell depending on the selection of light-handedness.
April 3, 2017: Advanced Materials
https://www.readbyqxmd.com/read/28319039/tunable-amplified-spontaneous-emission-in-graphene-quantum-dots-doped-cholesteric-liquid-crystals
#18
Mingxuan Cao, Siwei Yang, Yating Zhang, Xiaoxian Song, Yongli Che, Haiting Zhang, Yu Yu, Guqiao Ding, Guizhong Zhang, Jianquan Yao
Graphene quantum dots (GQDs) have received much research attention, because of their useful structure and optical absorption/emission. We report the tunable amplified spontaneous emission (ASE) in GQD-doped cholesteric liquid crystal (CLC), which to the best of our knowledge has not been previously observed. The GQDs are uniformly dispersed with a weight ratio of 0.5 wt.% in CLC. Under optical excitation, typical ASE is triggered in the system at pump energies greater than 1.25 mJ cm(-2). The emission peak at the long wavelength edge of the photonic bandgap shifts from 662 to 669 nm, as the working temperature is increased from 50 to 90 °C...
March 20, 2017: Nanotechnology
https://www.readbyqxmd.com/read/28297920/electric-field-induced-transport-of-microspheres-in-the-isotropic-and-chiral-nematic-phase-of-liquid-crystals
#19
Jiyoung Oh, Helen F Gleeson, Ingo Dierking
The application of an electric field to microspheres suspended in a liquid crystal causes particle translation in a plane perpendicular to the applied field direction. Depending on applied electric field amplitude and frequency, a wealth of different motion modes may be observed above a threshold, which can lead to linear, circular, or random particle trajectories. We present the stability diagram for these different translational modes of particles suspended in the isotropic and the chiral nematic phase of a liquid crystal and investigate the angular velocity, circular diameter, and linear velocity as a function of electric field amplitude and frequency...
February 2017: Physical Review. E
https://www.readbyqxmd.com/read/28241570/thickness-independent-dynamics-in-cholesteric-liquid-crystals
#20
Yo Inoue, Mayo Hattori, Hiroshi Moritake
We report fast electro-optic response independent of cell thickness in cholesteric liquid crystals (ChLCs). Usually, an electric field normal to the helix axis of ChLCs induces two fast and one slow response components: helical elongation (slow one), helical deformation (fast one), and flexoelectric effect (fast one). In this study, we found that a planarly aligned ChLC applied with an in-plane electric field exhibited only fast response components because the glass substrates suppressed the motion of the helical elongation...
February 20, 2017: Optics Express
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