Computer modelling of the director configuration in a supertwist nematic liquid crystal cell

Abstract

The director distribution in a supertwist nematic cell, containing La-Roche liquid crystal mixture 3010, has been studied extensively using Berreman's computer simulation approach. It is seen that the director distribution in the cell depends critically on the total twist angle θ_t, the surface tilt angle θ_o and the ratio of the cell thickness to the pitch d/p. The values of θ_o and φ_t have been optimized to yield a small bistability (ΔV = 0.06 V) and a relatively large change in the midplane tilt angle (Δθ_m = 51°) in an unstrained cell with ?_t = (d/p) × 360°. The optimum values of θ_o and Ø_t were found to be 15° and 240°, respectively. The effect of varying d/p on the director distribution has also been studied in great detail in supertwist cells with θ_o = 30° and Ø_t = 270°. Some interesting features in understrained and overstrained cells have been observed.     

Blue phase III widening in CE6-dispersed surface-functionalised CdSe nanoparticles

The phase transition behaviour of the chiral liquid crystal CE6 doped with spherical surface-functionalised CdSe nanoparticles has been examined by means of high-resolution adiabatic scanning calorimetry and polarising microscopy. The addition of nanoparticles results in an essentially stabilised blue phase III. The phase diagram is displayed upon heating and cooling and the enthalpy changes involved in the conversion between the blue phases are determined. The dispersion of functionalised nanoparticles is prominent for the stabilisation of blue phase III, which is potentially useful for applications, especially if applied on liquid crystals that exhibit blue phases close to room temperature.     

Cobalt(III) complexes of unsaturated carboxylic acids: synthesis, characterization, and photochemical studies in aqueous medium

Cobalt(III) ammine complexes coordinated to carboxylic acids are classic examples showing photoredox reactions originating from the ligand to metal charge transfer excited states. Cobalt(III) pentaammine complexes coordinated to unsaturated carboxylic acids as ligands were synthesized and characterized by spectroscopic methods. The photolysis of these complexes produces a carboxylate free radical. This free radical undergoes further transformation to form organic photoproducts. The organic photoproducts were characterized by spectroscopic methods. The nature of the decomposition products from the organic photoproduct was examined in detail. The quantum yields were also determined. The photochemical reactions have the potential to produce novel compounds from the decarboxylation of unsaturated acids, which shows interesting reaction pathways.     

Novel Tripod Amphiphiles for Membrane Protein Analysis

Integral membrane proteins play central roles in controlling the flow of information and molecules across membranes. Our understanding of membrane protein structures and functions, however, is seriously limited, mainly due to difficulties in handling and analysing these proteins in aqueous solution. The use of a detergent or other amphipathic agents is required to overcome the intrinsic incompatibility between the large lipophilic surfaces displayed by the membrane proteins in their native forms and the polar solvent molecules. Here, we introduce new tripod amphiphiles displaying favourable behaviours toward several membrane protein systems, leading to an enhanced protein solubilisation and stabilisation compared to both conventional detergents and previously described tripod amphiphiles.     

Influence of sputter power on structural and electrical properties of TiO2 films for Al/TiO2/Si gate capacitors

Titanium dioxide (TiO₂) thin films were deposited onto p‐Si substrates held at room temperature by reactive Direct Current (DC) magnetron sputtering at various sputter powers in the range 80–200 W. The as‐deposited TiO₂ films were annealed at a temperature of 1023 K. The post‐annealed films were characterized for crystallographic structure, chemical binding configuration, surface morphology and optical absorption. The electrical and dielectric properties of Al/TiO₂/p‐Si structure were determined from the capacitance–voltage and current–voltage characteristics. X‐ray diffraction studies confirmed that the as‐deposited films were amorphous in nature. After post‐annealing at 1023 K, the films formed at lower powers exhibited anatase phase, where as those deposited at sputter powers > 160 W showed the mixed anatase and rutile phases of TiO₂. The surface morphology of the films varied significantly with the increase of sputter power. The electrical and dielectric properties on the air‐annealed Al/TiO₂/p‐Si structures were studied. The effect of sputter power on the electrical and dielectric characteristics of the structure of Al/TiO₂/p‐Si (metal‐insulator‐semiconductor) was systematically investigated. Copyright © 2014 John Wiley & Sons, Ltd.     

Metal Complexes of Singly,Doubly and Triply Linked Porphyrins and Corroles: An Insight into the Physicochemical Properties

Metal complexes of multi-porphyrins and multi-corroles are unique systems that display a host of extremely interesting properties. Availability of free meso and β positions allow formation of different types of directly linked bis-porphyrins giving rise to intriguing optical and electronic properties. While the fields of metalloporphyrin and corroles monomer have seen exponential growth in the last decades, the chemistry of metal complexes of bis-porphyrins and bis-corroles remain rather underexplored. Therefore, the impact of covalent linkages on the optical, electronic, (spectro)electrochemical, magnetic and electrocatalytic activities of metal complexes of bis-porphyrins and -corroles has been summarized in this review article. This article shows that despite the (still) somewhat difficult synthetic access to these molecules, their extremely exciting properties do make a strong case for pursuing research on these classes of compounds.     

Electrochemical biosensors based on Ti3C2Tx MXene: future perspectives for on-site analysis

MXenes are recently developed two-dimensional layered materials composed of early transition metal carbides and/or nitrides that provide unique characteristics for biosensor applications. This review presents the recent progress made on the usage and applications of MXenes in the field of electrochemical biosensors, including microfluidic biosensors and wearable microfluidic biosensors, and highlights the challenges with possible solutions and future needs. The multilayered configuration and high conductivity make these materials as an immobilization matrix for the biomolecule immobilization with activity retention and to be explored in the fabrication of electrochemical sensors, respectively. First, how the MXene nanocomposite as an electrode modifier affects the sensing performance of the electrochemical biosensors based on enzymes, aptamer/DNA, and immunoassays is well described. Second, recent developments in MXene nanocomposites as wearable biosensing platforms for the biomolecule detection are highlighted. This review pointed out the future concerns and directions for the use of MXene nanocomposites to fabricate advanced electrochemical biosensors with high sensitivity and selectivity. Specifically, possibilities for developing microfluidic electrochemical sensors and wearable electrochemical microfluidic sensors with integrated biomolecule detection are emphasized.     

Recent Advancements on Immunomodulatory Mechanisms of Resveratrol in Tumor Microenvironment

Immunomodulation of the tumor microenvironment is emerging as an important area of research for the treatment of cancer patients. Several synthetic and natural agents are being investigated for their ability to enhance the immunogenic responses of immune cells present in the tumor microenvironment to impede tumor cell growth and dissemination. Among them, resveratrol, a stilbenoid found in red grapes and many other natural sources, has been studied extensively. Importantly, resveratrol has been shown to possess activity against various human diseases, including cancer. Mechanistically, resveratrol has been shown to regulate an array of signaling pathways and processes involving oxidative stress, inflammation, apoptosis, and several anticancer effects. Furthermore, recent research suggests that resveratrol can regulate various cellular signaling events including immune cell regulation, cytokines/chemokines secretion, and the expression of several other immune-related genes. In this review, we have summarized recent findings on resveratrol’s effects on immune regulatory cells and associated signaling in various cancer types. Numerous immunomodulatory effects of resveratrol suggest it may be useful in combination with other cancer therapies including immunotherapy for effective cancer management.     

Variable electron-phonon coupling in isolated metallic carbon nanotubes observed by Raman scattering

We report the existence of broad and weakly asymmetric features in the high-energy (G) Raman modes of freely suspended metallic carbon nanotubes of defined chiral index. A significant variation in peak width (from 12 cm(-1) to 110 cm(-1)) is observed as a function of the nanotube's chiral structure. When the nanotubes are electrostatically gated, the peak widths decrease. The broadness of the Raman features is understood as the consequence of coupling of the phonon to electron-hole pairs, the strength of which varies with the nanotube chiral index and the position of the Fermi energy.     

Slow light in bacteriorhodopsin solution using coherent population oscillations

Slow light is demonstrated in liquid phase in an aqueous bacteriorhodopsin (bR) solution at room temperature. Group velocity as low as 3 m/s (all the way to c) is achieved by exploiting the photoisomerization property of bR for coherent population oscillations. Slow light in the liquid phase offers several advantages over solids or vapors for a variety of applications: (i) shorter lifetimes of the M state facilitate slow light at higher modulation frequencies, (ii) convection makes it possible to obtain large signal delays even at high input powers, and (iii) solution concentration is another convenient parameter to vary the signal delay over a wide range.