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Ana R Fialho, Nelson R Bernardino, Nuno M Silvestre, Margarida M Telo da Gama
The confinement of liquid crystals inside curved geometries leads to exotic structures, with applications ranging from biosensors to optical switches and privacy windows. Here we study how curvature affects the alignment of a cholesteric liquid crystal. We model the system on the mesoscale using the Landau-de Gennes model. Our study was performed in three stages, analyzing different curved geometries from cylindrical walls and pores, to toroidal domains, in order to isolate the curvature effects. Our results show that the stresses introduced by the curvature influence the orientation of the liquid crystal molecules, and cause distortions in the natural periodicity of the cholesteric that depend on the radius of curvature, on the pitch, and on the dimensions of the system...
January 2017: Physical Review. E
Yunfeng Li, Elisabeth Prince, Sangho Cho, Alinaghi Salari, Youssef Mosaddeghian Golestani, Oleg D Lavrentovich, Eugenia Kumacheva
An important goal of the modern soft matter science is to discover new self-assembly modalities to precisely control the placement of small particles in space. Spatial inhomogeneity of liquid crystals offers the capability to organize colloids in certain regions such as the cores of the topological defects. Here we report two self-assembly modes of nanoparticles in linear defects-disclinations in a lyotropic colloidal cholesteric liquid crystal: a continuous helicoidal thread and a periodic array of discrete beads...
February 13, 2017: Proceedings of the National Academy of Sciences of the United States of America
Sung Hyun Yoo, Hee-Seung Lee
The wide range of fascinating supramolecular architectures found in nature, from DNA double helices to giant protein shells, inspires researchers to mimic the diverse shapes and functions of natural systems. Thus, a variety of artificial molecular platforms have been developed by assembling DNA-, peptide-, and protein-based building blocks for medicinal and biological applications. There has also been a significant interest in the research of non-natural oligomers (i.e., foldamers) that fold into well-defined secondary structures analogous to those found in proteins, because the assemblies of foldamers are expected not only to form biomimetic supramolecular architectures that resemble those of nature but also to display unique functions and unprecedented topologies at the same time due to their different folding propensities from those of natural building blocks...
February 13, 2017: Accounts of Chemical Research
Hui-Chen Yeh, Szu-Wei Lee
This paper reports on the emission characteristics of amino-functionalized graphene quantum dots (af-GQDs). We employed the variable stripe length method to measure the net optical gain of af-GQDs. Photoluminescence emission was enhanced through the efficient confinement of photons using an optical resonator. The two-dimensional resonator is made up of a cholesteric liquid crystal (CLC) reflector to enable the redistribution of spontaneous emission from the af-GQDs. The proposed method was shown to increase the intensity of peak emission to more than three times that of the reference sample without a CLC reflector...
January 23, 2017: Optics Express
Wen-Song Li, Yuan Shen, Zhi-Jie Chen, Qian Cui, Sen-Sen Li, Lu-Jian Chen
We evaluated the feasibility of embedding periodically arranged squares with planar and vertical texture into a background with a developable-modulation (DM) type cholesteric liquid crystal (CLC) fingerprint texture by a two-step ultraviolet-induced polymerization method. Checker-patterned optical diffractive elements, which can be seen as a variation of a two-dimensional (2D) barcode, were first realized and the dependence of diffraction behaviors on incident light polarization and applied voltage were investigated...
January 20, 2017: Applied Optics
Andrii Varanytsia, Liang-Chy Chien
We demonstrate a giant flexoelectro-optic behavior of liquid crystal dimer CB7CB. Flexoelectric properties of CB7CB experimentally characterized by measured angle of an in-plane rotation of helical axis (HA) in polymer stabilized uniform lying helix cholesteric liquid crystal. The 45° rotation of HA providing full intensity modulation of transmitted through a pair of crossed polarizers light, is achieved with 4.5 V/μm with a sub-millisecond electro-optic switching time. Reported properties enable application of CB7CB in applications of the flexoelectric effect in fast switching photonic and electro-optic devices...
January 24, 2017: Scientific Reports
Bruno Frka-Petesic, Harisoa Radavidson, Bruno Jean, Laurent Heux
Cellulose nanocrystal suspensions in apolar solvent spontaneously form iridescent liquid crystalline phases but the control of their macroscopic order is usually poor. The use of electric fields can provide control on the cholesteric orientation and its periodicity, allowing macroscopic sample homogeneity and dynamical tuning of their iridescent hues, and is demonstrated here.
January 23, 2017: Advanced Materials
Ruggero Cortini, Xiaolin Cheng, Jeremy C Smith
Electrostatic interactions between DNA molecules have been extensively studied experimentally and theoretically, but several aspects (e.g. its role in determining the pitch of the cholesteric DNA phase) still remain unclear. Here, we performed large-scale all-atom molecular dynamics simulations in explicit water and 150 mM sodium chloride, to reconstruct the potential of mean force (PMF) of two DNA oligomers 24 base pairs long as a function of their interaxial angle and intermolecular distance. We find that the potential of mean force is dominated by total DNA charge, and not by the helical geometry of its charged groups...
March 1, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Marian Chapran, Enrico Angioni, Neil J Findlay, Benjamin Breig, Vladyslav Cherpak, Pavlo Stakhira, Tell Tuttle, Dmytro Volyniuk, Juozas V Grazulevicius, Yuriy A Nastishin, Oleg D Lavrentovich, Peter J Skabara
A new interface engineering method is demonstrated for the preparation of an efficient white organic light-emitting diode (WOLED) by embedding an ultrathin layer of the novel ambipolar red emissive compound 4,4-difluoro-2,6-di(4-hexylthiopen-2-yl)-1,3,5,7,8-pentamethyl-4-bora-3a,4a-diaza-s-indacene (bThBODIPY) in the exciplex formation region. The compound shows a hole and electron mobility of 3.3 × 10(-4) and 2 × 10(-4) cm(2) V(-1) s(-1), respectively, at electric fields higher than 5.3 × 10(5) V cm(-1)...
January 24, 2017: ACS Applied Materials & Interfaces
Man-Yu Duan, Hui Cao, Yong Wu, Er-Li Li, Hui-Hui Wang, Dong Wang, Zhou Yang, Wan-Li He, Huai Yang
In this study, we demonstrate a novel method for fabricating polymer stabilized cholesteric liquid crystal (PSCLC) films with non-uniform pitch distribution by utilizing two kinds of photo-induced processes. Based on the large HTP temperature dependence of a chiral dopant, polymer networks were formed at two distant temperature points in sequence. The influence of the polymerization conditions on the reflectance properties of PSCLCs before and after polymerization was investigated. The results strongly suggest that the location and bandwidth of the reflection band can be controlled preferably by adjusting the ultraviolet light intensity and irradiation time of UV-light...
January 18, 2017: Physical Chemistry Chemical Physics: PCCP
Yuri M Yevdokimov, Sergey G Skuridin, Sergey V Semenov, Ljubov A Dadinova, Viktor I Salyanov, Efim I Kats
In this research, we observe and rationalize theoretically the transition from hexagonal to cholesteric packing of double-stranded (ds) DNA in dispersion particles. The samples were obtained by phase exclusion of linear ds DNA molecules from water-salt solutions of poly(ethylene glycol)-PEG-with concentrations ranging from 120 mg ml(-1) to 300 mg ml(-1). In the range of PEG concentrations from 120 mg ml(-1) to 220 mg ml(-1) at room temperature, we find ds DNA molecule packing, typical of classical cholesterics...
December 27, 2016: Journal of Biological Physics
Ping Liu, Xin Guo, Fuchun Nan, Yongxin Duan, Jianming Zhang
Iridescent films formed from the self-assembly of cellulose nanocrystals (CNCs) are brittle and difficult to handle or integrate within an industrial process. Here we present a simple approach to prepare iridescent CNC films with tunable pliability and coloration through the addition of ionic liquids (ILs) of 1-allyl-3-methylimidazolium chloride (AmimCl) as plasticizers. By using the undried CNC film as a filter membrane and ILs solution as a leaching liquid, it was found that the filtration process made ILs uniformly interpenetrate into CNC film due to the strong ionic interaction between CNC and AmimCl...
January 10, 2017: ACS Applied Materials & Interfaces
Mingxian Liu, Zhuohao Huo, Tengfei Liu, Yan Shen, Rui He, Changren Zhou
Highly ordered and concentric ring patterns consisting of halloysite nanotubes (HNTs) with hierarchical cholesteric architectures are prepared by evaporation induced self-assembly in a sphere-on-flat geometry. The structure and properties characters of HNTs are firstly investigated. HNTs show perfect tubular morphology in nanoscale with high dispersion stability in water. Upon drying HNTs aqueous suspension in a sphere-on flat confined space, regular concentric HNTs rings are formed on the substrate via a self-assembly process...
December 27, 2016: Langmuir: the ACS Journal of Surfaces and Colloids
P Rofouie, D Pasini, A D Rey
We present a model to investigate the formation of surface patterns in biological materials through the interaction of anisotropic interfacial tension, bending elasticity, and capillarity at their free surfaces. Focusing on the cholesteric liquid crystal (CLC) material model, the generalized shape equation for anisotropic interfaces using the Rapini-Papoular anchoring and Helfrich free energies is applied to understand the formation of multi-length scale patterns, such as those found in floral petals. The chiral liquid crystal-membrane model is shown to be analogous to a driven pendulum, a connection that enables generic pattern classification as a function of bending elasticity, liquid crystal chirality and anchoring strength...
January 18, 2017: Soft Matter
Takatsugu Endo, Shota Hosomi, Shunsuke Fujii, Kazuaki Ninomiya, Kenji Takahashi
We performed structural investigations of cellulose mixed with 1-ethyl-3-methylimidazolium acetate ([Emim][OAc]) in the entire concentration range (0-100 mol %) by wide-angle X-ray scattering with the aid of quantum chemical calculations and (13)C solid-state NMR spectroscopy. We particularly focused on a highly concentrated region (≥30 mol %), which has previously been overlooked. At concentrations of 15-30 mol %, a periodic peak corresponding to cellulose chain alignment emerged; this is associated with a lyotropic cholesteric liquid-crystalline phase...
December 15, 2016: Journal of Physical Chemistry Letters
Cornelia Rosu, Shane Jacobeen, Katherine Park, Elsa Reichmanis, Peter Yunker, Paul S Russo
Liquid crystals can organize dispersed particles into useful and exotic structures. In the case of lyotropic cholesteric polypeptide liquid crystals, polypeptide-coated particles are appealing because the surface chemistry matches that of the polymeric mesogen, which permits a tighter focus on factors such as extended particle shape. The colloidal particles developed here consist of a magnetic and fluorescent cylindrically symmetric silica core with one rounded, almost hemispherical end. Functionalized with helical poly(γ-stearyl-l-glutamate) (PSLG), the particles were dispersed at different concentrations in cholesteric liquid crystals (ChLC) of the same polymer in tetrahydrofuran (THF)...
December 13, 2016: Langmuir: the ACS Journal of Surfaces and Colloids
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 20, 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
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