Observation of lyotropic chromonic liquid crystals droplets with the perpendicular boundary condition

Department of PhysicsControlling anchoring conditions of liquid crystals (LCs) is crucial for the study of liquid crystals and development of liquid crystals-based displays and sensors. Although many studies have been made on thermotropic liquid crystals, the anchoring conditions of lyotropic chromonic liquid crystals (LCLCs) are difficult to control even through properties of LCLCs were actively studied. Conventional alignment methods have no effect on LCLCs, even work, anchoring is very weak. Only a few perpendicular alignment layers (a.k.a. homeotropic anchoring) in solid-LCs interfaces were reported through non-covalent interactions of hydrophobic polymer films and solid substrates such as graphene. However, the vertical alignment layers of LCLCs at the liquid interface has never been reported. We report, for the first time, the study of the homeotropic anchoring of liquid and LCLCs interfaces using hydrophobic oils without surfactants. As reported in thermotropic liquid crystals, a radial structure with a point defect has been found, but an unusual feature is the axial structure with ring disclination, which did not apply the external field. It implies that this anchoring strength is very weak anchoring conditions and another supporting evidence is the anchoring transition, which changes to the horizontal orientation from the perpendicular orientation. Also, because of the weak twist modulus of the LCLCs, the structure of the defects seemed to be twisted. This twist structure is consistent with previous reports. To observe the structures of homeotropic chiral nematic, brucine sulfate was used as a chiral dopants. Basically, we reproduced the director configurations of the droplets of the thermotropic chiral nematic LCs both with planar and homeotropic anchoring. Specifically, with the homeotropic anchoring, we noticed an increase in the effective helical pitch in the droplets according to the droplet size, i.e. the untwisting of the helical structure, which originates from the frustration of chiral nematic liquid crystals with the perpendicular boundary condition.ope

Planar Anchoring Strength And Pitch Measurements In Achiral And Chiral Chromonic Liquid Crystals Using 90-Degree Twist Cells

Chromonic liquid crystals are formed by molecules that spontaneously assemble into anisotropic structures in water. The ordering unit is therefore a molecular assembly instead of a molecule as in thermotropic liquid crystals. Although it has been known for a long time that certain dyes, drugs, and nucleic acids form chromonic liquid crystals, only recently has enough knowledge been gained on how to control their alignment so that studies of their fundamental liquid crystal properties can be performed. In this article, a simple method for producing planar alignment of the nematic phase in chromonic liquid crystals is described, and this in turn is used to create twisted nematic structures of both achiral and chiral chromonic liquid crystals. The optics of 90-degree twist cells allows the anchoring strength to be measured in achiral systems, which for this alignment technique is quite weak, about 3 x 10(-7) J/m2 for both disodium cromoglycate and Sunset Yellow FCF. The addition of a chiral amino acid to the system causes the chiral nematic phase to form, and similar optical measurements in 90-degree twist cells produce a measurement of the intrinsic pitch of the chiral nematic phase. From these measurements, the helical twisting power for L-alanine is found to be (1.1 +/- 0.4) x 10(-2) mu m(-1) wt%(-1) for 15 wt% disodium cromoglycate

Ortho-Fluorination of azophenols increases the mesophase stability of photoresponsive hydrogen-bonded liquid crystals

Photoresponsive liquid crystals (LCs) whose alignment can be controlled with UV-Visible light are appealing for a range of photonic applications. From the perspective of exploring the interplay between the light response and the self-assembly of the molecular components, supramolecular liquid crystals are of particular interest. They allow elaborating the structure-property relationships that govern the optical performance of LC materials by subtle variation of the chemical structures of the building blocks. Herein we present a supramolecular system comprising azophenols and stilbazoles as hydrogen-bond donors and acceptors, respectively, and show that ortho-fluorination of the azophenol dramatically increases the thermal stability of the LC phases, an important characteristics in their further utilization in photonics. The systems exhibit fast photoinduced order-disorder transitions, and rapid recovery of the liquid-crystalline state once the light irradiation is ceased, due to the photochemical properties of azophenols

Temperature-Phase Converter Based on a LC Cell as a Variable Capacitance

The main characteristic of liquid crystals is that their properties, both electrical and optical, can be modified through a convenient applied signal, for instance a certain voltage. This tunable behavior of liquid crystals is directly related to the orientation of their nanometric components with respect to a director direction. However, the initial alignment is a fabrication-dependent parameter and may be either planar or homeotropic. In addition, the strong dependence of the properties of liquid crystals with the temperature is well known and widely used for several temperature sensors. This dependence is produced by the influence of the temperature on the ordering of the molecules. In this work, we have studied the temperature dependence of the electric properties of a liquid crystal cell, in particular the dielectric permittivity, with the temperature as a function of the initial alignment set during the fabrication process. Starting from experimental measurements, an equivalent circuit model including the temperature dependence has been proposed. We have observed that a good linearity in a wide temperature range is provided at a suitable exciting frequency. Finally, a proper conditioner circuit is proposed as a powerful tool for linear and high sensibility temperature measurement.This work was supported by the Ministerio de Economía y Competitividad of Spain (grant No. TEC2013-47342-C2-2-R) and Comunidad de Madrid (SINFOTON-CM, reference P2013/MIT-2790)

Binary Mixture Composed of Nematic Liquid Crystal and Carbon Nanotubes: A Theoretical Description

Based on the phenomenological model first presented by van der Schoot et al., which predicts the alignment of carbon nanotube (CNT) dispersions in thermotropic nematic liquid crystals, we present the extensive results concerning the phase diagram and the orientational properties of the mixture in this chapter

Magnetically Actuated Liquid Crystals

Ferrimagnetic inorganic nanorods have been used as building blocks to construct liquid crystals with optical properties that can be instantly and reversibly controlled by manipulating the nanorod orientation using considerably weak external magnetic fields (1 mT). Under an alternating magnetic field, they exhibit an optical switching frequency above 100 Hz, which is comparable to the performance of commercial liquid crystals based on electrical switching. By combining magnetic alignment and lithography processes, it is also possible to create patterns of different polarizations in a thin composite film and control over the transmittance of light in particular areas. Developing such magnetically responsive liquid crystals opens the door toward various applications, which may benefit from the instantaneous and contactless nature of magnetic manipulation

In-Plane Retardation Switching Behavior at Certain Types of Smectic Liquid Crystals

Smectic liquid crystals’ layer structures and their influence on electro-optic characteristic properties are studied. Some background research works have revealed that a certain type of tilted smectic liquid crystal to the smectic layer normal showed some distorted out-of-plane retardation change. With intentional distortion of out-of-plane retardation change even provides almost in-plane only retardation change. In a certain type of smectic liquid crystal and its specific alignment condition, such a certain type of smectic liquid crystal panel shows in-plane only retardation switching. A more comprehensive study is still required, and such type of smectic liquid crystal panel provides unique electro-optic properties that have not been reported

Web-based interface system for bedside monitor

From face-to-face consultation to medicine at a distance, technology is changing the way medical services are delivered to the people. We are going into an era where the information is being digitized to be stored in a database. This is done in order to reduce information overlap and redundancy that are the main problems the health care sector are facing right now. More hospitals in other more advanced countries are going paperless. In order to provide better services to the critically ill patients in the ICU or CCU, a data acquisition program is developed for the acquisition of vital signs monitored in the critical care units. This work discusses the work done in extracting the data and signal from patient monitor BSM 8800 to the computer. The data are acquired using RS232C Interface Protocol. The vital signs acquired include oxygen saturation (SaCh), heart rate (HR), electrocardiograph (ECG) signal, non-invasive blood pressure (NIBP), respiration rate (RR), temperature (TEMP) and end tidal carbon dioxide (PETCO2 or ETCO2). Ventricular Premature Contraction (VPC), ST level and arrhythmia information are also acquired and displayed to provide a more thorough information on the condition of the patients. Alarm detection is also programmed so that in critical conditions the vital signs will be displayed in red for extra caution. An ECG user control is designed and embedded in the web page in order to convert and plot the ECG waveform from hexadecimal values sent from the bedside monitor. The user control has been tested its accuracy and proved its validity to reconstruct the original ECG waveform. Basic patient information can also be seen from the graphical user interface (GUI) that has been developed. Physicians and medical practitioners have to register with the system before gaining access to the system and only the physician-in-charge of the patient can see the more intricate details of the patient

Properties of the Broad-Range Nematic Phase of a Laterally Linked H-Shaped Liquid Crystal Dimer

In search for novel nematic materials, a laterally linked H-shaped liquid crystal dimer have been synthesized and characterized. The distinct feature of the material is a very broad temperature range (about 50 oC) of the nematic phase, which is in contrast with other reported H-dimers that show predominantly smectic phases. The material exhibits interesting textural features at the scale of nanometers (presence of smectic clusters) and at the macroscopic scales. Namely, at a certain temperature, the flat samples of the material show occurrence of domain walls. These domain walls are caused by the surface anchoring transition and separate regions with differently tilted director. Both above and below this transition temperature the material represents a uniaxial nematic, as confirmed by the studies of defects in flat samples and samples with colloidal inclusions, freely suspended drops, X-ray diffraction and transmission electron microscopy.Comment: 30 pages (including Supplementary Information), 7 Figure