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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
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 12, 2017: Soft Matter
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
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
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
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
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
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...
April 12, 2017: Advanced Materials
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
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
Mingxuan Cao, Siwei Yang, Yating Zhang, Xiaoxian Song, Yongli Che, Haiting Zhang, Yu Yu, Gu Ding, Guizhong Zhang, Jianquan Yao
Graphene quantum dots (GQDs) have received great attention owing to their unique structure and novel phenomena of optical absorption/emission. In this letter, we observed the tunable amplified spontaneous emission (ASE) in GQDs doped cholesteric liquid crystals (CLC) for the first time. The GQDs are dispersed in CLC homogeneously with the weight ratio of 0.5 wt%. Under optical excitation, a typical ASE is triggered in the system above a 1.25 mJ/cm2 threshold. In addition, the emission peak at the long wavelength edge of the photonic bandgap shifts from 662 nm to 669 nm with the change of working temperature...
March 20, 2017: Nanotechnology
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
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
Yujian Sun, Yanzi Gao, Le Zhou, Jianhua Huang, Hua Fang, Haipeng Ma, Yi Zhang, Jie Yang, Ping Song, Cuihong Zhang, Lanying Zhang, Fasheng Li, Yuzhen Zhao, Kexuan Li
In this study, a polymer dispersed cholesteric liquid crystal (PDChLC) film obtained via a one-step fabrication technique based on photopolymerization of a thiol-acrylate reaction system was prepared and characterized for the first time. The effects of the chiral dopant, the influence of thiol monomer functionality and content on the morphology and subsequent performance of the PDChLC films were systematically investigated. It was demonstrated that the addition of a small amount of chiral dopant slightly increased the driving voltage, but decreased the off-state transmittance significantly...
February 22, 2017: Molecules: a Journal of Synthetic Chemistry and Natural Product Chemistry
Wanshu Zhang, Lanying Zhang, Xiao Liang, Le Zhou, Jiumei Xiao, Li Yu, Fasheng Li, Hui Cao, Kexuan Li, Zhou Yang, Huai Yang
High-performance and cost-effective laser protection system is of crucial importance for the rapid advance of lasers in military and civilian fields leading to severe damages of human eyes and sensitive optical devices. However, it is crucially hindered by the angle-dependent protective effect and the complex preparation process. Here we demonstrate that angle-independence, good processibility, wavelength tunability, high optical density and good visibility can be effectuated simultaneously, by embedding dichroic anthraquinone dyes in a cholesteric liquid crystal matrix...
February 23, 2017: Scientific Reports
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 28, 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
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