Anisotropic Liquid Crystal Research Articles

Flexoelectric in-plane switching (IPS) mode with ultra-high-transmittance, low-voltage, low-frequency, and a flicker-free image.

The demands for a power-saving mode for displaying static images are ubiquitous not only in portable devices but also in price tags and advertising panels. At a low-frequency driving in liquid crystal displays (LCDs) for low-power consumption, the flexoelectric effect arises even in calamitic liquid crystals and the optical appearance of this physical phenomenon is found to be unusually large, being noticed as an image-flickering. Although the inherent integrated optical transmittance of in-plane switching (IPS) mode is relatively lower than that of fringe-field switching (FFS) mode, the IPS mode shows no static image-flickering but an optical spike (the so-called optical bounce), at the transient moment between signal positive and negative frames. Here, we demonstrate an IPS mode using negative dielectric anisotropy of liquid crystals (Δε < 0) and fine-patterned electrodes (the width w of and the space l between electrodes ≤ 3 μm) with reduced operation voltage (up to 40.7% to a conventional FFS mode with Δε < 0), reduced optical bounce (up to 4.4%. to a conventional FFS mode with Δε < 0) and enhanced transmittance (up to 32.1% to a conventional IPS mode with Δε > 0). We believe the result will contribute not only to the scientific understanding of the optical appearance of flexoelectric effect but also pave the way for engineering of a superior low-power consumption LCD.

Morphology of elastic nematic liquid crystal membranes.

Liquid crystalline phases found in many biological materials, such as actin, DNA, cellulose, and collagen can be responsible for the deformation of cell membranes. In this paper, cell membrane deformation is investigated through the coupling between liquid crystal anisotropy and membrane bending elasticity. The generalized shape equation for anisotropic interfaces, which resort to the Cahn-Hoffman capillarity vector, the Rapini-Papoular anchoring energy, and the Helfrich elastic energy, is applied to gain insight into the deformation of closed liquid crystal membranes. This study presents a general morphological phase diagram of membrane surface patterns, in which two characteristic regimes of membrane shapes can be classified with respect to the most dominant factor between liquid crystal anisotropy and bending elasticity. To that end, we consider a 2D nematic liquid crystal droplet immersed in a isotropic phase in the presence of an interfacial layer of surfactants, which leads to an additional elastic contribution to the free energy of the system. The presented results indicate that, depending on the bending elasticity of the cell membrane, the liquid crystal might be able to deform the cell, thereby resulting in anisotropic asymmetric shapes. As liquid crystal anisotropy dominates the bending elasticity, spindle-like or tactoid shapes, which are extensively observed in experiments, can be formed. The findings provide a foundational framework to better understand membrane topologies in living soft matters. Furthermore, the coupling between order and curvature of membranes shed new light into the design of novel functional soft materials.

Lyotropic Liquid Crystal Formed in Aqueous Lecithin Solutions with IPM and AEO20 Additives

Abstract The phase behavior and rheological properties of a lyotropic liquid crystal formed in the lecithin/AEO20/IPM/H2O system were investigated by means of phase diagram, polarized optical microscopy and rheology techniques at 37°C. After adding polyoxyethylene-20-oleyl ether (AEO20) and isopropyl myristate (IPM) to lecithin solutions, an isotropic liquid phase and an anisotropic liquid crystal phase were found. By analyzing the shear viscosity (η γ=0.1) and yield stress (σ 0), with increase in water content, the η γ=0.1 and σ 0 increase firstly and then decrease; with increasing IPM content, a decrease in the η γ=0.1 and σ 0 is observed. Notably, at the relatively higher water content area, the water content has little effect on the η γ=0.1 and critical stress. When the lecithin/AEO20 mass ratio is 1:2, the liquid crystal phase displays a stronger shear resistance and more stable network structure.

Freedericksz transition in smectic-A liquid crystals doped by ferroelectric nanoparticles

The structure, orientation and physical properties of liquid crystals is significantly affected by doping of ferroic (ferromagnetic and ferroelectric) nanoparticles into liquid crystals. Behavior of these suspensions in external fields depends on anchoring energy, volume fraction of doped nanoparticles, and sign of dielectric anisotropy of liquid crystals as well as relative orientation of director and local polarization of nanoparticles. Here, the threshold voltage for molecular reorientation (Freedericksz transition) is estimated theoretically in smectic-A liquid crystals doped by spherical ferroelectric nanoparticles, near the smectic-A to smectic-C transition temperature taking into account local electric field effects. It is shown that the threshold voltage is decreased by doping ferroelectric nanoparticles into liquid crystals.

Polarization Observations of Adsorption Behavior of Fatty Acids Using Optical Anisotropy of Liquid Crystal

Chemical interactions and formation of adsorbed films of additives strongly affect the tribological behavior in boundary lubrication. In order to examine the relationship between the adsorption behavior and friction properties of fatty acids, polarization observations using a liquid crystal and friction measurements were performed. A nematic liquid crystal [4-pentyl-4′-cyanobiphenyl (5CB)] and normal fatty acids with 16–22 C chains were base fluid and additive, respectively. The adsorption behavior of the fatty acids was observed using polarization microscopy and analyzing the optical anisotropy of 5CB. The adsorbed film of fatty acids induced a change in the orientation of 5CB from planar to homeotropic. The expansion speed of the homeotropic domain increased as the chain length of the fatty acid decreased. The friction coefficient of the test lubricants was measured in a steel–steel sliding contact using a low-speed reciprocating tribometer. At the first cycle of reciprocating sliding motion, the lower friction coefficient was measured using fatty acids with the shorter alkyl chain length. The friction coefficient at the first cycle showed a strong correlation with the expansion speed of the homeotropic domain. These results show that the shorter-chain fatty acids form an adsorbed film highly oriented perpendicular to the solid surface, and the adsorbed film provides a lower friction coefficient at the first cycle.

All-optical transistor- and diode-action and logic gates based on anisotropic nonlinear responsive liquid crystal.

In this paper, we show that anisotropic photosensitive nematic liquid crystals (PNLC) made by incorporating anisotropic absorbing dyes are promising candidates for constructing all-optical elements by virtue of the extraordinarily large optical nonlinearity of the nematic host. In particular, we have demonstrated several room-temperature ‘prototype’ PNLC-based all-optical devices such as optical diode, optical transistor and all primary logic gate operations (OR, AND, NOT) based on such optical transistor. Owing to the anisotropic absorption property and the optical activity of the twist alignment nematic cell, spatially non-reciprocal transmission response can be obtained within a sizeable optical isolation region of ~210 mW. Exploiting the same mechanisms, a tri-terminal configuration as an all-optical analogue of a bipolar junction transistor is fabricated. Its ability to be switched by an optical field enables us to realize an all-optical transistor and demonstrate cascadability, signal fan-out, logic restoration, and various logical gate operations such as OR, AND and NOT. Due to the possibility of synthesizing anisotropic dyes and wide ranging choice of liquid crystals nonlinear optical mechanisms, these all-optical operations can be optimized to have much lower thresholds and faster response speeds. The demonstrated capabilities of these devices have shown great potential in all-optical control system and photonic integrated circuits.

Bridging the terahertz near-field and far-field observations of liquid crystal based metamaterial absorbers**Project supported by the National Basic Research Program of China (Grant No. 2012CB921803), the National Natural Science Foundation of China (Grants Nos. 61225026, 61490714, 11304151, and 61435008), the Natural Science Foundation of Jiangsu Province, China (Grant Nos. BK20150845 and 15KJB140004), the Open Foundation Project of National Laboratory of

Metamaterial-based absorbers play a significant role in applications ranging from energy harvesting and thermal emitters to sensors and imaging devices. The middle dielectric layer of conventional metamaterial absorbers has always been solid. Researchers could not detect the near field distribution in this layer or utilize it effectively. Here, we use anisotropic liquid crystal as the dielectric layer to realize electrically fast tunable terahertz metamaterial absorbers. We demonstrate strong, position-dependent terahertz near-field enhancement with sub-wavelength resolution inside the metamaterial absorber. We measure the terahertz far-field absorption as the driving voltage increases. By combining experimental results with liquid crystal simulations, we verify the near-field distribution in the middle layer indirectly and bridge the near-field and far-field observations. Our work opens new opportunities for creating high-performance, fast, tunable, terahertz metamaterial devices that can be applied in biological imaging and sensing.

Significant Enhancement of the Chiral Correlation Length in Nematic Liquid Crystals by Gold Nanoparticle Surfaces Featuring Axially Chiral Binaphthyl Ligands.

Chirality is a fundamental scientific concept best described by the absence of mirror symmetry and the inability to superimpose an object onto its mirror image by translation and rotation. Chirality is expressed at almost all molecular levels, from single molecules to supramolecular systems, and present virtually everywhere in nature. Here, to explore how chirality propagates from a chiral nanoscale surface, we study gold nanoparticles functionalized with axially chiral binaphthyl molecules. In particular, we synthesized three enantiomeric pairs of chiral ligand-capped gold nanoparticles differing in size, curvature, and ligand density to tune the chirality transfer from nanoscale solid surfaces to a bulk anisotropic liquid crystal medium. Ultimately, we are examining how far the chirality from a nanoparticle surface reaches into a bulk material. Circular dichroism spectra of the gold nanoparticles decorated with binaphthyl thiols confirmed that the binaphthyl moieties form a cisoid conformation in isotropic organic solvents. In the chiral nematic liquid crystal phase, induced by dispersing the gold nanoparticles into an achiral anisotropic nematic liquid crystal solvent, the binaphthyl moieties on the nanoparticle surface form a transoid conformation as determined by imaging the helical twist direction of the induced cholesteric phase. This suggests that the ligand density on the nanoscale metal surfaces provides a dynamic space to alter and adjust the helicity of binaphthyl derivatives in response to the ordering of the surrounding medium. The helical pitch values of the induced chiral nematic phase were determined, and the helical twisting power (HTP) of the chiral gold nanoparticles calculated to elucidate the chirality transfer efficiency of the binaphthyl ligand capped gold nanoparticles. Remarkably, the HTP increases with increasing diameter of the particles, that is, the efficiency of the chirality transfer of the binaphthyl units bound to the nanoparticle surface is diminished as the size of the particle is reduced. However, in comparison to the free ligands, per chiral molecule all tested gold nanoparticles induce helical distortions in a 10- to 50-fold larger number of liquid crystal host molecules surrounding each particle, indicating a significantly enhanced chiral correlation length. We propose that both the helicity and the chirality transfer efficiency of axially chiral binaphthyl derivatives can be controlled at metal nanoparticle surfaces by adjusting the particle size and curvature as well as the number and density of the chiral ligands to ultimately measure and tune the chiral correlation length.

Induced Magnetic Anisotropy in Liquid Crystals Doped with Resonant Semiconductor Nanoparticles

Currently, there are many efforts to improve the electrooptical properties of liquid crystals by means of doping them with different types of nanoparticles. In addition, liquid crystals may be used as active media to dynamically control other interesting phenomena, such as light scattering resonances. In this sense, mixtures of resonant nanoparticles hosted in a liquid crystal could be a potential metamaterial with interesting properties. In this work, the artificial magnetism induced in a mixture of semiconductor nanoparticles surrounded by a liquid crystal is analyzed. Effective magnetic permeability of mixtures has been obtained using the Maxwell-Garnett effective medium theory. Furthermore, permeability variations with nanoparticles size and their concentration in the liquid crystal, as well as the magnetic anisotropy, have been studied.

Electrically tunable infrared reflector with adjustable bandwidth broadening up to 1100 nm

A tunable infrared reflector has been fabricated using polymer stabilized cholesteric liquid crystals containing a negative dielectric, anisotropic liquid crystal and a long and flexible ethylene glycol twin crosslinker.

Light scattering by a nematic liquid crystal droplet: Wentzel–Kramers–Brillouin approximation

Light scattering by an optically anisotropic liquid crystal (LC) droplet of a nematic in an isotropic polymer matrix is considered in the Wentzel–Kramers–Brillouin (WKB) approximation. General relations are obtained for elements of the amplitude matrix of light scattering by a droplet of arbitrary shape and for the structure of the director field. Analytic expressions for the amplitude matrices are derived for spherical LC droplets with a uniformly oriented structure of local optical axes for strictly forward and strictly backward scattering. The efficiency factors of extinction and backward scattering for a spherical nonabsorbing LC droplet depending on the LC optical anisotropy, refractive index of the polymer, illumination conditions, and orientation of the optical axis of the droplet are analyzed. Verification of the obtained solutions has been performed.

Colloidal interactions in a homeotropic nematic cell with different elastic constants.

We propose a theoretical description of the interaction mediated by a nematic-liquid-crystal host with different Frank elastic constants. A general expression for the energy of such an interaction between colloidal particles of arbitrary size and shape suspended in a homeotropic cell is obtained. In the cells of large thickness, the presented potential converges to that found previously for small particles in the nematic bulk. In general, our results confirm the validity of the one-constant approximation for weakly elastically anisotropic nematic liquid crystals. For nematics with a high splay-to-bend ratio we predict a larger range of the interaction. Using the dependence of this range on the elastic constants, we show that there exists a qualitative similarity between the interactions in a nematic and in a smectic-A phase. It manifests itself, in particular, in a decrease of the angle between a chain of quadrupole particles and the uniform far-field director across a nematic-smectic-A phase transition. We also demonstrate that the anisotropy of the elastic constants can lead to the formation of thermodynamically stable linear superstructures of asymmetric particles (elastic monopoles) with large, compared to usual dipole chains, interparticle distances.

Surfactant-doped reverse-mode polymer-dispersed liquid crystal display with enhanced properties

ABSTRACTIn this article, a nonionic surfactant Brij30 has been used to vertical align the negative anisotropic liquid crystal. The surfactant is further used in reverse-mode polymer-dispersed liquid crystal display to enhance the electro-optical properties. This work shows an enhancement of contrast ratio simply with the addition of surfactant. In addition, contact angle and surface free energies have been determined to judge the role of surfactant in control of surface orientation of liquid crystal molecules.

3A02 ネマティック液晶中における分子配向性マイクロ粒子の電界応答機構の解明(ソフトマター,口頭発表,2015年日本液晶学会討論会)

3A02 ネマティック液晶中における分子配向性マイクロ粒子の電界応答機構の解明(ソフトマター,口頭発表,2015年日本液晶学会討論会)

A novel tunable microwave filter integrated power dividers using liquid crystal

ABSTRACTThis article presents design considerations of a tunable microwave filter integrated power divider based on highly anisotropic liquid crystals (LCs), which helps to reduce the circuit size. The proposed device comprising a thin LC layer between a ground plane and a directly coupled inverted microstrip line exhibits the equal power splitting function with a tunable bandpass response. The integrated device results in sharp rejection and smaller circuit area, as compared with the cascaded connection of an equal power divider and tunable microwave filter. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:2539–2543, 2015

On the conducting sheath double-helix loaded liquid crystal optical fibers

This work presents analysis of wave propagation in a rather new type of three-layer optical fiber wherein the outermost region being composed of radially anisotropic liquid crystal, and conducting sheath helix loadings exist at the core–inner clad as well as the inner clad–outer liquid crystal clad interfaces. The fiber structure offers two-way control on wave propagation through it. Focus is, however, made on the wave confinements in fiber due to the helix structures, as characterized by the respective pitch angles. Specific values of helix pitch angles at the two layer interfaces are taken into account, and the confinement patterns are analyzed. The dominant property of sheath helix structure over confinement patterns is quite an obvious fact. Clearly, the helix pitch angle greatly controls over the power confinement characteristics, which can be altered upon suitable adjustments of helical windings. Treatments have been made to illustrate the power patterns in all possible scenarios for critical pitch variations in each layer interface.

Fabrication and Characterization of Liquid Crystal Waveguides in PDMS Channels for Optofluidic Applications

We present our recent experimental results on the fabrication and the characterization of PDMS rectangular channel waveguides infiltrated with a nematic liquid crystal. Optical characterization of waveguide structures with three different widths recently implemented are reported. The particular molecular alignment inside PDMS waveguide allows polarization independent propagation despite liquid crystal anisotropy. Soft material technology based on PDMS used to fabricate liquid crystal channel waveguides is low cost and easy to implement, allowing to obtain any geometry.

Hierarchical Striped Walls Constructed by the Photopolymerization of Discotic Reactive Building Blocks in the Anisotropic Liquid Crystal Solvents

A triphenylene-based reactive mesogenic molecule (abbreviated as HABET) was newly designed and synthesized as a programmed building block to construct the striped walls by the photopolymerization in the anisotropic liquid crystal (LC) solvents. On the basis of thermal, scattering and microscopic analyses, it was found that HABET formed three ordered structures: a columnar hexagonal LC phase (ΦH), a tilted columnar hexagonal LC phase (ΦT) and a highly ordered columnar oblique crystal phase (ΦOK). The microscopic molecular orientations in the hierarchical superstructures were controlled in the anisotropic LC solvents with the help of surface anchoring forces, while the dimensions of the striped wall morphologies were determined by the patterned photomasks. The long axis of self-assembled columns in the striped walls was perpendicular to the surface alignment direction regardless of the photomask direction. Additionally, it was realized that the shapes of water drops as well as the surface water contact angles can be tuned by the hierarchical superstructures and morphologies of the polymerized HABET networks. The anisotropic hierarchical superstructures and morphologies concurrently fabricated during the polymerization in the anisotropic LC medium can offer a potential pathway for liquid transportation in the microfluidic devices.

Model-free estimation of the effective correlation time for C-H bond reorientation in amphiphilic bilayers: (1)H-(13)C solid-state NMR and MD simulations.

Molecular dynamics (MD) simulations give atomically detailed information on structure and dynamics in amphiphilic bilayer systems on timescales up to about 1 μs. The reorientational dynamics of the C-H bonds is conventionally verified by measurements of (13)C or (2)H nuclear magnetic resonance (NMR) longitudinal relaxation rates R1, which are more sensitive to motional processes with correlation times close to the inverse Larmor frequency, typically around 1-10 ns on standard NMR instrumentation, and are thus less sensitive to the 10-1000 ns timescale motion that can be observed in the MD simulations. We propose an experimental procedure for atomically resolved model-free estimation of the C-H bond effective reorientational correlation time τe, which includes contributions from the entire range of all-atom MD timescales and that can be calculated directly from the MD trajectories. The approach is based on measurements of (13)C R1 and R1ρ relaxation rates, as well as (1)H-(13)C dipolar couplings, and is applicable to anisotropic liquid crystalline lipid or surfactant systems using a conventional solid-state NMR spectrometer and samples with natural isotopic composition. The procedure is demonstrated on a fully hydrated lamellar phase of 1-palmitoyl-2-oleoyl-phosphatidylcholine, yielding values of τe from 0.1 ns for the methyl groups in the choline moiety and at the end of the acyl chains to 3 ns for the g1 methylene group of the glycerol backbone. MD simulations performed with a widely used united-atom force-field reproduce the τe-profile of the major part of the acyl chains but underestimate the dynamics of the glycerol backbone and adjacent molecular segments. The measurement of experimental τe-profiles can be used to study subtle effects on C-H bond reorientational motions in anisotropic liquid crystals, as well as to validate the C-H bond reorientation dynamics predicted in MD simulations of amphiphilic bilayers such as lipid membranes.

Research progress on preparation, manipulation, and remote sensing applications of high-order orbital angular momentum of photons

Photons are an ideal candidate for encoding both classical and quantum information. Besides spin angular momentum associated with circular polarization, single photon can also carry other fundamentally new degree of freedom of orbital angular momentum related to the spiral phase structure of light. The key significance of orbital angular momentum lies in its potential in realizing a high-dimensional Hilbert space and in encoding a high-dimensional quantum information. Since Allen et al. [Allen L, Beijersbergen M W, Spreeuw R J C, Woerdman J P 1992 Phys. Rev. A 45 8185] recognized the physical reality of photon orbital angular momentum in 1992, rapidly growing interest has been aroused in orbital angular momentum (OAM) from both classical and quantum points of view. Here we present an overall review on the high-order orbital angular momentum of photon, including its preparation and manipulation based on some specific techniques and also its applications. The spatial light modulator is a commercial device that has been widely employed to generate the OAM beams. We make and identify the optical OAM superposition with very high quantum numbers up to l=360. Recently, the metallic spiral phase mirrors were also developed to produce high-order OAM beams up to l=5050. In addition, the Q-plates made of anisotropic and inhomogeneous liquid crystals were invented to generate high-order OAM beams in a polarization-controllable manner, and the OAM superposition of l=± 50 were achieved. Owing to high rotational symmetry, these high OAM beams have been found to have more and more important applications in the fields of high-sensitivity sensing and high-precision measurements. Two fascinating examples are discussed in detail. The first example is that the research group led by Prof. Zeilinger has prepared and observed the quantum entanglement of high orbital angular momenta up to l=±300 by the technique of polarization-OAM entanglement swapping, and they demonstrated that the angular resolution could be significantly improved by a factor of l. Their result was the first step for entangling and twisting even macroscopic, spatially separated objects in two different directions. The second example is that the research group led by Prof. Padgett has demonstrated an elegant experiment of rotational Doppler effects for visible light with l=±20 OAM superposition. They showed that a spinning object with an optically rough surface might induce a Doppler effect in light reflected from the direction parallel to the rotation axis, and the frequency shift was proportional to both the disk's angular speed and the optical OAM. The potential applications in noncontact measurement of angular speed and in significant improvement of angular resolution for remote sensing will be particularly fascinating.