Measuring Thickness and Pretilt in Reflective Vertically Aligned Nematic Liquid Crystal Displays

Pretilt angle is a parameter of the utmost importance in the ultimate performance of vertically-aligned negative nematic LC displays. When these devices work in reflective mode, as is the LCOS microdisplays, accurate measurement of pretilt angles becomes a difficult problem, since usual experimental setups based on retardation of the polarization components of the impinging light are proportional to the product effective birefringence (neff - no) times thickness, and any attempt to separate these variables is cancelled out by symmetry. This work shows a relatively simple method capable of separating both variables. An experimental setup specifically aimed at vertically aligned reflective cells has been prepared. At the same time, a simulation model has been developed taking into account the properties of actual reflective displays. Comparison between experimental and theoretical results shows some discrepancies that can be explained assuming that the LC profile contains a residual twist. Including that twist in the model, an excellent agreement between theory and experiment has been achieved. Matching of simulations and measurements yields to the separate determination of pretilt angle and thickness and gives good estimates for the residual twist angle

Security devices based on liquid crystals doped with a colour dye

Liquid crystal properties make them useful for the development of security devices in applications of authentication and detection of fakes. Induced orientation of liquid crystal molecules and birefringence are the two main properties used in security devices. Employing liquid crystal and dichroic colorants, we have developed devices that show, with the aid of a polarizer, multiple images on each side of the device. Rubbed polyimide is used as alignment layer on each substrate of the LC cell. By rubbing the polyimide in different directions in each substrate it is possible to create any kind of symbols, drawings or motifs with a greyscale; the more complex the created device is, the more difficult is to fake it. To identify the motifs it is necessary to use polarized light. Depending on whether the polarizer is located in front of the LC cell or behind it, different motifs from one or the other substrate are shown. The effect arises from the dopant colour dye added to the liquid crystal, the induced orientation and the twist structure. In practice, a grazing reflection on a dielectric surface is polarized enough to see the effect. Any LC flat panel display can obviously be used as backlight as well

Caracterización de la membrana NF-97 mediante disoluciones salinas. Aplicacióndel modelo de Spiegler-Kedem-Kachalsky

Los procesos fÍsicos basados en las tecnologÍas de membrana se muestran como una clara alternativa en el campo de la desalinización y tratamiento de aguas. Un paso previo en el diseño de estos procesos consiste en la selección y caracterización de las membranas que van a ser utilizadas, siendo estos ensayos de gran utilidad para predecir el comportamiento de las mismas durante su posterior empleo. En este trabajo se ha caracterizado, mediante el uso de dos disoluciones salinas distintas, la membrana de nanofiltración de poliamida (NF-97), al objeto de obtener sus condiciones óptimas de funcionamiento. Los resultados obtenidos se han ajustado al modelo de transporte de flujo a través de la membrana de Spiegler-Kedem-Katchalsky, determinando, mediante resolución gráfica, las constantes del mismo. Se ha comprobado que el modelo es adecuado para describir el proceso de eliminación de las sales mediante nanofiltración, lo que permite predecir el comportamiento de la membrana en otras condiciones de operación

V-Shape Liquid Crystal-Based Retromodulator Air to Ground Optical Communications

This paper describes the use of a 2D liquid crystal retro-modulator as a free space, wireless, optical link. The retro-modulator is made up of a retro-reflecting cornercube onto which 2 cascaded V-shape smectics liquid crystal modulators are mounted. The communication link differs with respect to more conventional optical links in not using amplitude (nor frequency) modulation, but instead state-of-polarisation (SOP) modulation known as Polarisation Shift Keying (PolSK). PolSK has the advantage over amplitude modulation, that it is less sensitive to changes in the visibility of the atmosphere, and increases inherently the bandwidth of the link. The implementation of PolSK both in liquid crystal based and in retro-modulated communication are novelties

Synthesis and Properties of High Tilted Antiferroelectric Esters with Partially Fluorinated Alkoxyalkoxy Terminal Chains

Novel chiral esters with partially fluorinated alkoxyalkoxy terminal chains are described. Their phase transition temperatures, enthalpies, and electrooptical properties are reported. A helical pitch in pure compounds and their mixtures based on selective reflection of light is also characterized

Nematic liquid crystal reorientation around multi-walled carbon nanotubes mapped via Raman microscopy

We have studied the formation of topological defects in liquid crystal (LC) matrices induced by multiwalled carbon nanotubes (MWCNTs) and external electric fields. The defects are ascribable to a distortion of the LC molecular director in proximity of the MWCNT surface. The system is analyzed macroscopically using spectroscopic variable angle ellipsometry. Concurrently, confocal micro-Raman spectroscopy is used to study the system state at the microscale. This allows to acquire a three-dimensional, spatially-resolved map of the topological defect, determining scale length variations and orientation topography of the LC molecules around the MWCNT

Electrooptic characterization of tunable cylindrical liquid crystal lenses

In this work, one-dimensional arrays of cylindrical adaptive liquid crystal lenses were manufactured and characterized; and test devices were filled with nematic liquid crystal. Comb interdigitated electrodes were designed as a mask pattern for the control electrode on the top glass substrates. A radial graded refractive index along each microsized lens was achieved by fabricating a layer of high resistance sheet deposited as a control electrode. These tunable lenses were switched by applying amplitude and frequency optimized waveforms on the control electrode. Phase profiles generated by the radial electric field distribution on each lens were measured by a convectional interferometric technique

Patients' perceptions on shared decision making during prescription of subcutaneous biological drug treatments for inflammatory arthritis: the RHEU-LIFE survey

Short report[Abstract] Objectives: The aim of this study was to explore the preferences of patients with rheumatic diseases and their perceived experience regarding participation in shared decision making (SDM) when they were prescribed a subcutaneous (SC) biological drug. Methods: A printed survey was handed to 1,000 patients with inflammatory rheumatic diseases treated with SC biological drug. The survey included closed questions about preferences regarding decision making and about patients' experience when they were prescribed an SC biological drug. Descriptive statistics were performed with stratification by patient profiles, using chi-square for comparisons between groups. Results: A total of 592 surveys were received (response rate 59.2%, mean age 51.7 years, 57.6% women). Some 28.2% of patients reported preferring to take part in treatment selection, a percentage that was higher in younger patients, in those with higher academic degree and in those who search information in sources different to that of health care professionals. Over half of patients (56.3%) perceived that the rheumatologist considered their opinion when prescribing an SC biological drug, a percentage higher in younger people. Only in 40.8% of cases did the patients' preference match their perception of their participation in the process. No differences were observed by sex, disease or number of biologics. Conclusions: Patients with inflammatory rheumatic diseases want information about their treatments but mostly leave the prescription decision to the rheumatologist. Younger people, or those with higher academic degree, more often want to participate in the SDM. There are discrepancies between patient preferences and perceptions of this process

Cymantrene–Triazole "Click" Products: Structural Characterization and Electrochemical Properties

We report the first known examples of triazole-derivatized cymantrene complexes (η5-[4-substituted triazol-1-yl]cyclopentadienyl)tricarbonylmanganese(I), obtained via a “click” chemical synthesis, bearing a phenyl, 3-aminophenyl, or 4-aminophenyl moiety at the 4-position of the triazole ring. Structural characterization data using multinuclear NMR, UV–vis, ATR-IR, and mass spectrometric methods are provided, as well as crystallographic data for (η5-[4-phenyltriazol-1-yl]cyclopentadienyl)tricarbonylmanganese(I) and (η5-[4-(3-aminophenyl)triazol-1-yl]cyclopentadienyl)tricarbonylmanganese(I). Cyclic voltammetric characterization of the redox behavior of each of the three cymantrene–triazole complexes is presented together with digital simulations, in situ infrared spectroelectrochemistry, and DFT calculations to extract the associated kinetic and thermodynamic parameters. The trypanocidal activity of each cymantrene–triazole complex is also examined, and these complexes are found to be more active than cymantrene alone