Search results for "Liquid-crystal"
showing 10 items of 27 documents
Mesomorphic and electrooptical properties of viologens based on non-symmetric alkyl/polyfluoroalkyl functionalization and on an oxadiazolyl-extended …
2019
Two different sets of ionic liquid crystals based on bistriflimide salts of non-symmetrically substituted polyfluorinated bipyridinium (viologens) and bent symmetrically substituted dialkyl-oxadiazolyl-bipyridinium have been synthesized, in order to study the effect on the mesomorphic and electrooptical properties of the non-symmetric functionalization (alkyl chain and fluoroalkyl chains of different lengths) on the two pyridinium rings and additionally the effect of a bent conjugated spacer among the two pyridinium units of the viologen. POM and DSC characterization show that the synthesized salts have a mesomorphic and, in some cases, polymesomorphic behaviour in a wide thermal range, als…
Localized Liquid Secretion from a Photopatterned Liquid-Crystal Polymer Skin
2020
Liquid-releasing artificial skins are made from films made of a smectic liquid-crystal polymer network (LCN) photopolymerized in the presence of a photoactive azobenzene chromophore and a liquid-crystal porogen. The nonreactive porogen phase separates during the polymerization process, and the polymer forms a spongy polymer network filled with liquid. The liquid is excreted from the film when exposed to UV light upon conversion of trans-azobenzene to its cis isomer. Here, localized liquid secretion at preset positions at the polymer film is described. The design principle is based on creating a hybrid molecular architecture with both smectic and nonordered isotropic alignments in a continuo…
Nanostructured CdO thin films for water treatments
2016
Abstract CdO was the very first transparent conducting metal oxide discovered. CdO thin films show electrical and optical properties of interest as photosensitive anode materials for photochemical cells, phototransistors, photodiodes, window electrodes in liquid crystal displays, IR detectors, antireflection coatings, gas sensors and in other solar energy applications. In the present study we report on the spectroscopic, microscopic, electrical and photo-catalytic properties of CdO thin films prepared by a metal organic chemical vapor method. The degenerate semiconducting CdO thin films are useful as photocatalysts for water treatments.
Low-cost, portable open-source gas monitoring device based on chemosensory technology
2015
[EN] We report herein the construction of an electronic device to perform the real-time digitalization of the color state of the optical chemosensors used in the detection of dangerous gases. To construct the device, we used open-source modular electronics, such as Arduino and Sparkfun components, as well as free and open-source software (FOSS). The basic principle of the operation of this device is the continuous color measurement of a chemosensor-doped sensing film, whose color changes in the presence of a specific gas. The chemosensor-sensing film can be prepared by using any of the widely available chemosensors for the desired gas. Color measurement is taken by two TCS230 color sensor I…
Spin crossover star-shaped metallomesogens of iron(II).
2014
Three new types of spin crossover (SCO) metallomesogens of Fe-II based on symmetric tripod ligands and their magnetic and structural properties are reported here. These were obtained by condensation of tris(2-aminoethyl)-amin (tren) with the aldehyde derived from 3-alkoxy-6-methylpyridine (mpyN, N (number of carbon atoms in n-alkyl chains) = 8, 18), 1-alkyl-1H-imidazole (imN, N = 4, 16, 18, 20, 22), or 1-alkyl-1H-benzimidazole (bimN, N = 6, 14, 16, 18, 20). A complex derived from 1-octadecyl-1H-naphtho[2,3-d]imidazole (nim18) retains the high spin state at any temperature. Single crystals of the short-chain complexes were investigated by a combination of X-ray crystallography, magnetic meas…
Generalized formulation and symmetry properties of reciprocal nonabsorbing polarization devices: Application to liquid-crystal displays
2000
We present a general formulation based on the Jones-matrix theory for reciprocal nonabsorbing polarization devices, including polarization interference filters and liquid-crystal displays. The development of this formulation is based on general symmetry conditions that relate the Jones matrix when the device is illuminated from the front side and from the back side. The application to liquid-crystal displays results in a constraint of the Jones-matrix elements, which represents a generalization of the existing models that explain their modulation properties.
Twist angle determination in liquid crystal displays by location of local adiabatic points
1998
In this work we present a method for the determination of the twist angle of an arbitrary twisted nematic liquid crystal spatial light modulator. The method is based on the location of local adiabatic points, i.e., situations in which the liquid crystal SLM acts only as a rotation device. For these cases, the rotation induced on the polarization of the incident beam is equal to the twist angle. Consequently, the twist angle can be determined with high precision. We show that local adiabatic regime may be achieved in two ways, either by changing the incident beam wavelength, or by applying a voltage to the electrodes of the display. However, the simple model that describes the SLM in the off…
Reconfigurable Shack-Hartmann sensor without moving elements.
2010
We demonstrate wavefront sensing with variable measurement sensitivity and dynamic range by means of a programmable microlens array implemented onto an off-the-shelf twisted nematic liquid crystal display operating as a phase-only spatial light modulator. Electronic control of the optical power of a liquid lens inserted at the aperture stop of a telecentric relay system allows sensing reconfigurability without moving components. Results of laboratory experiments show the ability of the setup to detect both smooth and highly aberrated wavefronts with adequate sensitivity.
Transparent Boundary Condition for Oseen-Frank Model. Application for NLC Cells With Patterned Electrodes
2015
In the present work a novel application of Transparent Boundary Conditions (TBC) to nematic liquid crystal cells (NLCC) with planar alignment and a patterned electrode is studied. This device is attracting great interest since it allows soliton steering by optically and externally induced waveguides. We employ the continuum Oseen-Frank theory to find the tilt and twist angle distributions in the cell under the one-constant approximation. The electric field distribution takes into account the whole 2D permittivity tensor for the transverse coordinates. Standard finite difference time domain methods together with an iterative method is applied to find an approximate solution to our coupled pr…
Supramolecular hierarchy among halogen and hydrogen bond donors in light-induced surface patterning
2015
Halogen bonding, a noncovalent interaction possessing several unique features compared to the more familiar hydrogen bonding, is emerging as a powerful tool in functional materials design. Herein, we unambiguously show that one of these characteristic features, namely high directionality, renders halogen bonding the interaction of choice when developing azobenzene-containing supramolecular polymers for light-induced surface patterning. The study is conducted by using an extensive library of azobenzene molecules that differ only in terms of the bond-donor unit. We introduce a new tetrafluorophenol-containing azobenzene photoswitch capable of forming strong hydrogen bonds, and show that an io…