Use Of Liquid Crystals Research Articles

Design of Responsive and Active (Soft) Materials Using Liquid Crystals.

Liquid crystals (LCs) are widely known for their use in liquid crystal displays (LCDs). Indeed, LCDs represent one of the most successful technologies developed to date using a responsive soft material: An electric field is used to induce a change in ordering of the LC and thus a change in optical appearance. Over the past decade, however, research has revealed the fundamental underpinnings of potentially far broader and more pervasive uses of LCs for the design of responsive soft material systems. These systems involve a delicate interplay of the effects of surface-induced ordering, elastic strain of LCs, and formation of topological defects and are characterized by a chemical complexity and diversity of nano- and micrometer-scale geometry that goes well beyond that previously investigated. As a reflection of this evolution, the community investigating LC-based materials now relies heavily on concepts from colloid and interface science. In this context, this review describes recent advances in colloidal and interfacial phenomena involving LCs that are enabling the design of new classes of soft matter that respond to stimuli as broad as light, airborne pollutants, bacterial toxins in water, mechanical interactions with living cells, molecular chirality, and more. Ongoing efforts hint also that the collective properties of LCs (e.g., LC-dispersed colloids) will, over the coming decade, yield exciting new classes of driven or active soft material systems in which organization (and useful properties) emerges during the dissipation of energy.

Use of liquid crystal to study the interactions of alkyl polyglycosides with gelatin and bovine serum albumin

Abstract In this study, liquid crystal (LC) was used to study the interactions of alkyl polyglycosides (APG) with gelatin and bovine serum albumin (BSA) at the LC-aqueous interface. The LC easily undergo an orientational transition from a homeotropic to a planar state after proteins were in contact to the LC-aqueous interface decorated with APG, thus inducing an optical change from dark to bright. The optical image analysis reveals that the rearrangement rate of APG monolayer is tightly dependent on the concentration and chemical structure of the protein of interest. For example, the rearrangement rate of APG monolayer increases with an increasing gelatin concentration. We also find that the chemical structure of the proteins has a significant impact on the difference in the growth behavior of bright domains in LC.

Anisotropic Shear Viscosity of Photoaligned Liquid Crystal Confined in Submicrometer-to-Nanometer-Scale Gap Widths Revealed with Simultaneously Measured Molecular Orientation.

In the context of the use of liquid crystals (LCs) as lubricants and lubricant additives, this study investigates the anisotropic shear viscosity of LCs confined in nanometer-sized gap widths subject to both shearing and photoalignment. The photoalignment is achieved using anisotropically dimerized polyvinyl cinnamate (PVCi) films coated on substrates. We simultaneously measure the viscosity and order parameter of a liquid crystal (4-cyano-4'-pentylbiphenyl) confined and sheared in the gap range of 500 nm down to a few nm. We achieve this simultaneous measurement using an original method that combines a highly sensitive viscosity measurement and a sensitive birefringence measurement. When the LC is sheared in the same direction as the photoalignment (parallel shearing), the order parameter, which is around 0.3 in the bulk state, increases up to around 0.4 at a gap width of less than 50 nm and the viscosity is smaller than half the bulk viscosity. We consider that this increase in the order parameter is due to the highly ordered photoaligned LC layer near the PVCi film, and the viscosity decrease is due to shear thinning of this layer enhanced by both confinement and molecular ordering. In addition, we observe a gradual decrease in viscosity starting at a gap of less than around 300 nm in the parallel shearing. Based on the apparent slip model, we show that the LC layer near the PVCi film can also cause this gradual viscosity decrease. In contrast, when the LC is sheared in the direction perpendicular to the photoalignment direction (perpendicular shearing), the viscosity increases as the gap decreases. We speculate that this is due to the rotational motion of the LC molecules caused by the competing effect of shear alignment and photoalignment. We believe our findings can significantly contribute to a better understanding of the confined LCs utilized for lubrication.

Use of liquid crystals for imaging different inclusion abilities of α-cyclodextrin and β-cyclodextrin toward cetyltrimethyl ammonium bromide

We herein report a method for the imaging of different inclusion abilities of α-cyclodextrin (α-CD) and β-cyclodextrin (β-CD) toward cetyltrimethyl ammonium bromide (CTAB) using liquid crystals (LCs). The optical transition from the dark to the bright state was caused by the inclusion interaction between CTAB and CDs. It was confirmed that α-CD formed more stable CTAB complexes than β-CD, leading to different optical responses of the LCs from the α-CD/CTAB and β-CD/CTAB systems. This method could be used to provide a visual method for selection of the correct CD molecules for interaction with surfactant molecules in recognition systems.

Liquid crystal polaroid glass electrode from e-waste for synchronized removal/recovery of Cr+6 from wastewater by microbial fuel cell

This study demonstrates the use of Liquid Crystal coated Polaroid Glass Electrode (LCPGE) material collected from disposed liquid–crystal display (LCD) computer monitor as electrodes in microbial fuel cell (MFC) for the simultaneous reduction/recovery of Cr+6 from chromium wastewater. Fourier transform infrared spectrum (FT-IR) confirms the presence of NH2, CN, CO and OC and/or COC functional groups in LCPGE. An excellent electrochemical performance with distinct redox peaks were observed in cyclic voltammetry test (100mV/s). The maximum current density of 110mA/m2 (10mW/m2) was achieved by operating MFC in batch mode. At the cathode LCPGE (10.5cm2) interface, toxic Cr+6 ions readily accepted electrons and formed nontoxic Cr2O3 as confirmed by FT-IR and X-ray photoelectron spectroscopy analysis. Moreover, electrochemical impedance analysis shows that bacteria were readily attached to the surface of LCPGE (10.5cm2) within 24h in a Bioelectrochemical System (BES).

An UV‐curable epoxy acrylate oligomer with high refractive index containing fluorene: Preparation, characterization, and application

ABSTRACTIn this article, a novel UV‐curable epoxy acrylate oligomer (BPEFPGMA) with high refractive index is successfully prepared through semi‐esterification reaction of 9,9‐bis[4‐(2‐hydroxyethoxy)phenyl]fluorene and phthalic anhydride, followed by end‐caping of glycidyl methacrylate. After 15 times’ repetitions, the process and properties of this oligomer are stable and reliable. The resulting BPEFPGMA exhibited low solvent content (≤1600 ppm), low viscosity (1900–2500 mPa s at 60°C), high refractive index (1.587 ± 0.003 at 20°C), and normal Mw (2550–3536 g/mol). The coating formulations of 1.57 UV‐curable glue are mixed with BPEFPGMA as reactive oligomer. Through the technology of UV‐curing forming, the corresponding brightness enhancement films are obtained. The resulting films exhibit normal structure, excellent adhesion (5B), good scratch resistance (50 g), and good abrasion resistance (50 g). They show excellent performance, and have reached the quality standard for use in liquid crystal display industry. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42386.

Nanomorphology of Polymer Blends for a Light-Scattering Thermosetting Plate Based on Self-Assembly

An approach to optical plate production using the nanomorphology of polymer blends in light-scattering thermosetting plates based on self-assembly was investigated without using the conventional approach of blending nanoparticles such as silica sol, zirconia sol, phosphor, or chromophore into the polymer matrix. For this purpose, two specified polymers having carboxylic acid and epoxy groups were blended using a light-emitting diode for use in liquid crystal displays. The developed light-scattering thermosetting plate containing poly(acrylic acid) with the carboxylic acid at four different weight average molecular weights in a cycloaliphatic epoxy polymer was shown to achieve regular nanoparticles of 30–350 nm for light-scattering, light-scattering rates of over 10% at a wavelength of 300 nm, a thermal stability up to 230 °C, O2 gas barrier properties approximately 50 times smaller than that of polyethylene, and solvent resistance after polymerizing.

Liquid crystal dual-mode band-pass filter with improved performance

AbstractOver the last twenty years, there has been a growing interest in the design of tunable devices at microwave frequencies by us- ing liquid crystals technology. In particular, the use of liquid crystals with high dielectric anisotropy allows manufacturing voltage-controlled devices to operate in a wide frequency range. In this work the frequency response of a liquid crystal band-pass filter with dual-mode microstrip structure has been studied in depth by using a simulation software tool. A reshap- ing of a conventional dual-mode square patch resonator bandpass filter with a square notch, studied in the literature, has been proposed with the goal of improving the filter performance. The main features achieved are a significant increase in the return loss of the filter and a narrowing of a 3-dB bandwidth. Specifically, a reduction in the filter bandwidth from 800 MHz to 600 MHz, which leads to a return loss increase from 6 dB to 12.5 dB, has been achieved. The filter centre frequency can be tuned from 4.54 GHz to 5.19 GHz.

GaInN-based light emitting diodes embedded with wire grid polarizers

The use of liquid crystal displays (LCDs) has become prevalent in our modern, technology driven society. We demonstrate a linearly polarized GaInN light-emitting diode (LED) embedded with a wire-grid polarizer (WGP). A derivation of rigorous coupled-wave analysis is given; starting from Maxwell’s equations and finishing by matching the boundary conditions in the grating and other regions of interest. Simulated results are shown for various grating parameters, including different metals used for the grating and the metal-line dimensions. An LED fabrication process is developed for demonstrating WGP-LEDs. A clear polarization preference for the light coming out of the WGP-LED is experimentally demonstrated with a polarization ratio over 0.90, which is in good agreement with simulation results.

Ultr a thin Color Filter for Wearable Displays and Multispectral Imaging

We present a new approach to making in-pixel color filters for a wearable display such as LCOS (liquid crystal on silicon) or a DLP (digital light processing) system. Unlike current color filters or methods used in these devices, our approach enables Red-Green-Blue (RGB) color images using color filters fabricated using semiconductor ultra-thin film. These filters are less than 100 nm thick, making them better suited to integration with light modulators than traditional pigment-based filters. Additionally, these films are fabricated via e-beam evaporation or RF sputtering, which is compatible with most modern chip manufacturing. In this paper, we present the design concept for these filters, including simulation results that demonstrate improved liquid crystal control when using these filters, demonstrate an example RGB filter array and also present an enhanced structure which could meet requirements of DLP based multispectral imaging. This is the first time the use of these filters is presented for use in liquid crystal based displays and DLP.

An Autostereoscopic Device for Mobile Applications Based on a Liquid Crystal Microlens Array and an OLED Display

In recent years, many experimental and theoretical research groups worldwide have actively worked on demonstrating the use of liquid crystals (LCs) as adaptive lenses for image generation, waveform shaping, and non-mechanical focusing applications. In particular, important achievements have concerned the development of alternative solutions for 3D vision. This work focuses on the design and evaluation of the electro-optic response of a LC-based 2D/3D autostereoscopic display prototype. A strategy for achieving 2D/3D vision has been implemented with a cylindrical LC lens array placed in front of a display; this array acts as a lenticular sheet with a tunable focal length by electrically controlling the birefringence. The performance of the 2D/3D device was evaluated in terms of the angular luminance, image deflection, crosstalk, and 3D contrast within a simulated environment. These measurements were performed with characterization equipment for autostereoscopic 3D displays (angular resolution of 0.03 $^{\circ}$ ).

Liquid crystal electrography: Electric field mapping and detection of peak electric field strength in AlGaN/GaN high electron mobility transistors

The liquid crystal mixture E7, based on cyanobiphenyl, has been successfully employed to map electric field strength and distribution in AlGaN/GaN high electron mobility transistors. Using a transmitted light image through crossed polarizers the optical response of the liquid crystal deposited onto the surface of the devices was recorded as a function of source–drain bias, Vds. At a critical voltage of 4V the preferred direction of orientation of the long axes of the liquid crystal molecules in the drain access region aligned with one of the polarizers resulting in reduced transmitted light intensity. This indicates that at this electric field strength molecule orientation in most of the liquid crystal film is dominated by the electric field effect rather than the influence of surface anchoring. The experimental results were compared to device simulations. Electric field strength above the surface at Vds=4V was simulated to reach or exceed 0.006MV/cm. This electric field is consistent with the field expected for E7 to overcome internal elastic energy. This result illustrates the usefulness of liquid crystals to directly determine and map electric fields in electronic devices, including small electric field strengths.

Antibody-free Detection of Human Chorionic Gonadotropin by Use of Liquid Crystals

Human chorionic gonadotropin (hCG) is an important biomarker for the diagnosis of pregnancy and cancers. In this study, we report an antibody-free and label-free mechanism for detecting hCG. To replace enzyme-labeled antibodies, we use a short oligopeptide as an hCG receptor to bind hCG. The short oligopeptide sequence, (N-)PPLRINRHILTR(-C), is identified after 5 rounds of screening by use of a phage library. After binding, liquid crystal (LC) is used to transduce the binding event into optical signals. The captured hCG can disrupt a thin layer (~6 μm) of LC covered on the surface. Depending on the initial concentration of hCG, LC gives distinct optical signals visible to the naked eye. The limit of detection (LOD) for this method is approximately 1 IU/mL (2 nM) in both phosphate-buffered saline and urine samples, and only 0.6 μL of hCG solution is required. This means that as little as 45.5 pg of hCG can be detected by this method. Compared to other detection methods for hCG, this detection method does not require the use of antibody and is label-free. It has the potential to become a portable diagnostic kit for hCG.

Liquid crystals: a new approach for latent heat storage

SUMMARY The development of thermal storage systems adapted to processes in which steam is involved is currently increasing because no cost-effective solution is available to date. Entailing water condensation and evaporation, isothermal storage under latent heat is the most appropriate approach. The low thermal conductivity of the materials currently in use significantly affects both power density and power generation of the storage system in discharge. In order to solve these drawbacks, the use of liquid crystals as alternative storage materials is proposed because they can absorb/release energy at constant temperature and at the same time keep the ability to flow. In this way, liquid crystals with clearing points close to the saturated steam working temperature and high enthalpy of mesophase-isotropic liquid transition would be required. The main advantage of using liquid crystals as storage materials is that convection would be the heat transfer mechanism and power would be constant with time during discharge processes. Copyright © 2013 John Wiley & Sons, Ltd.

Ion Density Analysis of Single-Stranded DNA in Liquid Crystal

With the widespread use of liquid crystals (LCs) in liquid crystal displays, we have looked into the application of liquid crystals in biotechnology. The purpose of the study described here is to investigate the physical properties of DNA using LCs. Synthetic oligonucleotide molecules were dispersed in MLC6884, the sample injected into antiparallel cells, and the amount of mobile ions was measured. The LC cell doped with oligonucleotide molecules showed a sequence-dependent, specific correlation between oligonucleotide concentration and the amount of mobile ions in the LC cells. In the framework of the Stokes model and polyacrylamide gel electrophoresis (PAGE) analysis, we speculate that this result arises from the difference in ion mobility, which is caused by the shape of the oligonucleotide molecule in the LC.

Liquid Crystal-Based Emulsions for Synthesis of Spherical and Non-Spherical Particles with Chemical Patches

We report the use of liquid crystal (LC)-in-water emulsions for the synthesis of either spherical or non-spherical particles with chemically distinct domains located at the poles of the particles. The approach involves the localization of solid colloids at topological defects that form predictably at surfaces of water-dispersed LC droplets. By polymerizing the LC droplets displaying the colloids at their surface defects, we demonstrate formation of both spherical and, upon extraction of the mesogen, anisotropic composite particles with colloids located at either one or both of the poles. Because the colloids protrude from the surfaces of the particles, they also define organized, chemical patches with functionality controlled by the colloid surface.

An electromechanically reconfigurable plasmonic metamaterial operating in the near-infrared

Current efforts in metamaterials research focus on attaining dynamic functionalities such as tunability, switching and modulation of electromagnetic waves. To this end, various approaches have emerged, including embedded varactors, phase-change media, the use of liquid crystals, electrical modulation with graphene and superconductors, and carrier injection or depletion in semiconductor substrates. However, tuning, switching and modulating metamaterial properties in the visible and near-infrared range remain major technological challenges: indeed, the existing microelectromechanical solutions used for the sub-terahertz and terahertz regimes cannot be shrunk by two to three orders of magnitude to enter the optical spectral range. Here, we develop a new type of metamaterial operating in the optical part of the spectrum that is three orders of magnitude faster than previously reported electrically reconfigurable metamaterials. The metamaterial is actuated by electrostatic forces arising from the application of only a few volts to its nanoscale building blocks-the plasmonic metamolecules-that are supported by pairs of parallel strings cut from a flexible silicon nitride membrane of nanoscale thickness. These strings, of picogram mass, can be driven synchronously to megahertz frequencies to electromechanically reconfigure the metamolecules and dramatically change the transmission and reflection spectra of the metamaterial. The metamaterial's colossal electro-optical response (on the order of 10(-5)-10(-6) m V(-1)) allows for either fast continuous tuning of its optical properties (up to 8% optical signal modulation at up to megahertz rates) or high-contrast irreversible switching in a device only 100 nm thick, without the need for external polarizers and analysers.

Reconfigurable beams with arbitrary polarization and shape distributions at a given plane

Methods for generating beams with arbitrary polarization based on the use of liquid crystal displays have recently attracted interest from a wide range of sources. In this paper we present a technique for generating beams with arbitrary polarization and shape distributions at a given plane using a Mach-Zehnder setup. The transverse components of the incident beam are processed independently by means of spatial light modulators placed in each path of the interferometer. The modulators display computer generated holograms designed to dynamically encode any amplitude value and polarization state for each point of the wavefront in a given plane. The steps required to design such beams are described in detail. Several beams performing different polarization and intensity landscapes have been experimentally implemented. The results obtained demonstrate the capability of the proposed technique to tailor the amplitude and polarization of the beam simultaneously.

Mono-Stereo-Autostereo

In the past decade, surgery planning has changed significantly. The main reason is the improvements in computer graphical rendering power and display technology, which turned the plain graphics of the mid-1990s into interactive stereoscopic objects. To report our experiences with 2 virtual reality systems used for planning neurosurgical operations. A series of 208 operations were planned with the Dextroscope (Bracco AMT, Singapore) requiring the use of liquid crystal display shutter glasses. The participating neurosurgeons answered a questionnaire after the planning procedure and postoperatively. In a second prospective series of 33 patients, we used an autostereoscopic monitor system (MD20-3-D; Setred SA, Sweden) to plan intracranial operations. A questionnaire regarding the value of surgery planning was answered preoperatively and postoperatively. The Dextroscope could be integrated into daily surgical routine. Surgeons regarded their understanding of the pathoanatomical situation as improved, leading to enhanced intraoperative orientation and confidence compared with conventional planning. The autostereoscopic Setred system was regarded as helpful in establishing the surgical strategy and analyzing the pathoanatomical situation compared with conventional planning. Both systems were perceived as a backup in case of failure of the standard navigation system. Improvement of display and interaction techniques adds to the realism of the planning process and enables precise structural understanding preoperatively. This minimizes intraoperative guesswork and exploratory dissection. Autostereoscopic display techniques will further increase the value and acceptance of 3-dimensional planning and intraoperative navigation.

Synthesis and properties of allyloxy-based biphenyl liquid crystals with multiple lateral fluoro substituents

Allyloxy-based biphenyl liquid crystals, composed of alkyl chain, trans-cyclohexane and biphenyl mesogenic cores, ethylene linking groups, lateral fluoro substituents and allyloxy terminal groups were prepared via a six-step reaction based on 4-alkylcyclohexanecarbonitrile. Their structures were confirmed via infrared spectrometry, mass spectra and nuclear magnetic resonance. The mesomorphic properties of the present compounds were investigated by differential scanning calorimetry and polarising optical microscopy. The compounds exhibited negative dielectric anisotropy from −3.36 to −4.29 and a broad nematic mesophase with low melting points and high clearing points. The effects of the allyloxy terminal group and the lateral fluoro substituents on the mesomorphic properties and negative dielectric anisotropies are discussed. The present allyloxy-based biphenyl liquid crystals have potential for use in liquid crystal display mixtures.