Alignment and switching of AFLC materials using various boundary conditions

We have systematically studied the quality of bookshelf alignment and electro‐optic characteristics of two antiferroelectric liquid crystal materials in cells with various boundary conditions. The electro‐optic characteristics of the materials studied depend strongly on both the liquid crystal materials and the boundary conditions at the supporting substrates. We have compared a number of observations in these cells: the tendency to form AFLC domains in the virgin state and after switching; the surface electroclinic effect (SEC effect); the transmission–voltage characteristics (TV) when driven with triangular‐ and square‐wave voltages at various frequencies; the threshold field and the conditions for relaxation to the AFLC state. The set of samples includes specially designed and manufactured test cells with different polyimides as alignment layers, treated with varying rubbing strengths. We discuss the significance of various factors and show the importance of simultaneously optimizing both materials and cell parameters for AFLC applications.     

Simulations of energy and switching in AFLCDs with different boundary conditions

Using standard expressions for the various terms in the Gibbs free energy, the switching in antiferroelectric liquid crystal (AFLC) displays is simulated and the time evolution of various energy terms and of the liquid crystal director distributions are calculated. It is shown that when returning from a strong positive voltage to zero, one can reach two types of antiferroelectric state: the normal alternating state with the two bulk polarizations perpendicular to the electrodes and opposite to each other, and the alternative splayed symmetric state with two bulk polarizations parallel to the electrodes and again opposite to each other. The former case gives rise to tri-state switching characteristics, the latter to V-shaped switching. In general strong polar interaction with the alignment layer favours V-shaped switching while weak or no polar interaction give rise to tri-state switching characteristics. Since the V-shaped characteristic has so far only been demonstrated experimentally in ferroelectric liquid crystals (or antiferroelectric liquid crystals being in the ferroelectric state), the difference in AFLCs is discussed and the conditions for continuous switching are modelled. The simulations show that the switching characteristics of the antiferroelectric display can be controlled by the surface parameters.     

Ladder operators and boundary conditions

The factorization method, related to supersymmetry in quantum mechanics and Lie algebras, is revisited, and the representations and properties of ladder operators originated from “natural” and “nonnatural” boundary conditions is discussed. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 81: 141–147, 2001     

Alignment and switching of nematic liquid crystals embedded in porous chiral thin films

Porous thin films with engineered microstructures have been fabricated using glancing angle deposition (GLAD). GLAD films with chiral microstructures have been previously shown to exhibit unique chiral optical response. The pores of these films were embedded with (non-chiral) nematic liquid crystals (LCs) to produce a new composite optical material wherein the GLAD film induces chiral nematic-like LC orientation. We demonstrate here reversible electro-optic switching of the LC component of these hybrid films. Unaddressed, cells of GLAD/LC hybrid films show enhanced chiral optic response compared with the unfilled GLAD film. When addressed, the chiral optic response vanishes.     

An inter-calibration campaign using various selected Pu spike isotopic reference materials

In nuclear safeguards, precise and accurate isotopic analyses are needed for two major elements from the nuclear fuel cycle: uranium and plutonium. This can be achieved by Isotope Dilution Mass Spectrometry (IDMS), which is one of the most reliable analytical techniques for the determination of plutonium amount content to a high level of accuracy. In order to achieve reliable isotope measurements isotopic reference materials with certified amount of plutonium and isotopic composition are required. At the Institute for Reference Materials and Measurements (IRMM) various plutonium spike reference materials for isotopes ²³⁹Pu, ²⁴⁰Pu, ²⁴²Pu and ²⁴⁴Pu are available. This enabled the setup of an inter-calibration campaign inter-linking selected plutonium spikes on a metrological basis applying state-of-the-art measurement procedures. The aim of this campaign is threefold: firstly to perform measurements on selected plutonium spike isotopic reference materials for quality control purposes, secondly to verify the amount content and the isotopic composition of the recently produced IRMM-1027m large sized dried (LSD) spikes and thirdly to demonstrate IRMM’s measurement capabilities for plutonium analysis via external quality tools. The obtained results using various spike isotopic reference materials will be presented and discussed in this paper. The measurement uncertainties of the IDMS results were calculated according to the guide to the expression of uncertainty in measurement (GUM).     

Nonperiodic stochastic boundary conditions for molecular dynamics simulations of materials embedded into a continuum mechanics domain

A scheme is described for performing molecular dynamics simulations on polymers under nonperiodic, stochastic boundary conditions. It has been designed to allow later the embedding of a particle domain treated by molecular dynamics into a continuum environment treated by finite elements. It combines, in the boundary region, harmonically restrained particles to confine the system with dissipative particle dynamics to dissipate energy and to thermostat the simulation. The equilibrium position of the tethered particles, the so-called anchor points, are well suited for transmitting deformations, forces and force derivatives between the particle and continuum domains. In the present work the particle scheme is tested by comparing results for coarse-grained polystyrene melts under nonperiodic and regular periodic boundary conditions. Excellent agreement is found for thermodynamic, structural, and dynamic properties.     

Porous materials show superhydrophobic to superhydrophilic switching

Switching between superhydrophobicity and superhydrophilicity in porous materials was predicted theoretically and demonstrated experimentally with the example of thermally induced contact angle change; tunability of this system was also demonstrated.     

Enrichment of adenosine using thermally responsive chromatographic materials under friendly pH conditions

A thermally responsive boronate affinity chromatographic material, which showed thermal sensitivity, had been successfully applied for the enrichment and separation of cis‐diol‐containing compounds, and the capture and release process could be facilitated by adjusting the temperature. However, in this system, the pH of the mobile phase must be higher than 9.8, and alkaline media can lead to the degradation of labile compounds; the use of silica beads also limits its use. In this study, thermally responsive boronate affinity chromatographic material, namely poly(N‐isopropylacrylamide‐co‐N‐acryloyl‐3‐aminophenylboronic acid) grafted silica, was successfully prepared by atom transfer radical polymerization. Its structure was confirmed by IR spectroscopy and the graft ratio was 20.8%, determined by thermogravimetric analysis. Furthermore, the capture/release of adenosine, a cis‐diol, was performed from pH 5.0–9.0 and 10–50°C. The elution of adenosine was remarkably retarded at decreased temperatures and adenosine could be captured completely at 10°C at pH values of 5.0–9.0. The enrichment of adenosine could be achieved by simply changing the temperature from 10 to 50°C. Therefore, this material not only improved the stability of the silica, but was also suitable for the capture of oxidation‐sensitive biological analytes. Moreover, it could be used for the enrichment of cis‐diol‐containing compounds in LC with MS.     

New AFLC: a trimesogen presenting antiferroelectric smectic C phase (SmCA) and twist grain boundary smectic A phase (TGBA)

A first oligomeric antiferroelectric liquid crystal, a cyclohexane based trimesogen, was synthesized. It was characterized by microscopic observation, differential scanning calorimetry, helical pitch measurement, X-ray diffraction and electro-optical study. A large domain of antiferroelectric phase (DeltaT 55 C) and a very rich polymorphism (SmC*, SmC*, SmC* , A FI SmC*, TGBA, BP) are exhibited by the trimesogen.     

Fabrication and characterization of ordered microsized tubular TiO2 films by using various anodizing conditions

In this study, we investigated the oxidation process of titanium in two different electrolytic solutions in order to understand the effect of the electrolyte on the microsized tubular TiO₂ formation and their structure. In the first set of experiments, we used 0.5% HF electrolyte by applying 23?V for 50?min. The second set of experiments was performed using glycerol electrolyte with 0.27?M NH₄F and 1.5% H₂O under 40?V for 19?h. Both experiments were performed at room temperature. After the anodizing process, the samples were annealed at 550?°C in O₂ atmosphere. In both electrolytic conditions well-ordered microsized tubular TiO₂ were obtained. The morphologies, structures, and microsized tubular TiO₂ array films were characterized by FE-SEM, EDS, and XRD.     

Effects of various boundary conditions on the response of Poisson-Nernst-Planck impedance spectroscopy analysis models and comparison with a continuous-time random-walk model

Various electrode reaction rate boundary conditions suitable for mean-field Poisson-Nernst-Planck (PNP) mobile charge frequency response continuum models are defined and incorporated in the resulting Chang-Jaffe (CJ) CJPNP model, the ohmic OHPNP one, and a simplified GPNP one in order to generalize from full to partial blocking of mobile charges at the two plane parallel electrodes. Model responses using exact synthetic PNP data involving only mobile negative charges are discussed and compared for a wide range of CJ dimensionless reaction rate values. The CJPNP and OHPNP ones are shown to be fully equivalent, except possibly for the analysis of nanomaterial structures. The dielectric strengths associated with the CJPNP diffuse double layers at the electrodes were found to decrease toward 0 as the reaction rate increased, consistent with fewer blocked charges and more reacting ones. Parameter estimates from GPNP fits of CJPNP data were shown to lead to accurate calculated values of the CJ reaction rate and of some other CJPNP parameters. Best fits of CaCu(3)Ti(4)O(12) (CCTO) single-crystal data, an electronic conductor, at 80 and 140 K, required the anomalous diffusion model, CJPNPA, and led to medium-size rate estimates of about 0.12 and 0.03, respectively, as well as good estimates of the values of other important CJPNPA parameters such as the independently verified concentration of neutral dissociable centers. These continuum-fit results were found to be only somewhat comparable to those obtained from a composite continuous-time random-walk hopping/trapping semiuniversal UN model.     

Nonperiodic boundary conditions for solvated systems

The simulation of charged and/or strongly polar solutes represents a challenge for standard molecular-dynamics techniques. The use of periodic boundary conditions (PBCs) leads to artifacts due to the interaction between two replicas in the presence of the long-range Coulomb forces. A way to avoid these problems is the use of nonperiodic boundary conditions. A possible realization is to consider a finite system, a sphere, embedded in a reaction field described by the method of the images. In the present work the modified image approximation has been implemented in a molecular-dynamics code and optimized for the use of two standard solvents, water and acetonitrile. The methodology has then been applied to investigate the conformational changes in water-solvated alanine dipeptide. The free-energy surface calculated with this method is comparable to that obtained with PBC.     

Electrostatic potentials in periodic boundary conditions

We discuss the effects of using periodic boundary conditions on the statistical mechanics of particles with electrostatic interactions. For the system of particles with electrostatic interactions plus periodic boundary conditions we develop an effective interaction which may be used with ordinary boundary conditions. The lattice sums which arise from the periodic boundary conditions contain divergences. We use a variant of Ewald's method to evaluate the sums which makes the handling of the divergences fairly simple. We discuss the effect of the effective interaction on the thermodynamics of the system.     

On the possibility of using of materials based on adhesive prepregs in Arctic conditions

Analysis of the properties of adhesive prepregs, which were synthesized based on glass fabrics and carbon fillers, and materials made on their basis was performed. It was shown that the composite materials based on prepregs with VSK-14-2m binder surpass composite materials based on prepregs synthesized by the impregnation of fabrics with soluble binders in terms of physical and mechanical properties at–130°C, water resistance, hygroscopicity, and water absorption.     

Qualitative and quantitative contents of organic acids in multivitamin plant raw materials studied using various physicochemical methods

Russian Chemical Bulletin - The results of qualitative analysis of organic acids in multivitamin mixtures No. 1 and No. 2 are presented. The contents of malic, citric, and ascorbic acids were...     

INAA and flame AAS of various vegetable reference materials

Summary INAA and flame AAS have been used for the analysis of a large number of vegetable reference materials. Out of all determined elements (28 by INAA and 11 by AAS) nine are common for both methods (Ca, Cd, Co, Cu, Fe, Mg, Mn, Na, Zn) and for these the possibilities of the two methods have been compared.     

A quantitative study of tethered chains in various solution conditions using Langmuir diblock copolymer monolayers

This article summarizes our investigations of tethered chain systems using Langmuir monolayers of poly(dimethylsiloxane)‐polystyrene (PDMS‐PS) diblock copolymers on organic liquids. In this system, the PDMS block adsorbs strongly to the air surface while the PS block dangles into the subphase liquid. The air surface can be made either repulsive or attractive for the tethered PS chain segments by choosing a subphase liquid which has a surface tension less than or greater than that of PS, respectively. The segment profile of the PS block is determined by neutron reflection as a function of the surface density, the molecular weights of the PS and PDMS blocks, and the solution conditions. We cover the range of reduced surface density (Σ ) characteristic of the large body of data in the literature for systems of chains tethered onto solid surfaces from dilute solution in good or theta solvent conditions (Σ < 12). We emphasize quantitative comparisons with analytical profile forms and scaling predictions. We find that the strong‐stretching limit assumed in analytical self‐consistent field calculations (SCF) and scaling theories is not valid over this Σ range. On the other hand, over a large portion of this range (Σ ⪇ 5) tethered chain profiles are well described by a renormalization group theory for weakly interacting or noninteracting chains. Simultaneous with the study of the profile form, the free energy of the tethered chains is examined through the surface tension. A strong increase in the surface pressure is observed with increasing surface density which determines the maximum surface density which can be achieved. This effect is attributed to a combination of higher order osmotic interactions and configurational constraints. This effect may explain several outstanding discrepancies regarding the adsorption of end‐functionalized chains and diblock copolymers onto solid surfaces.     

Determination of water traces in various organic solvents using Karl Fischer method under FIA conditions

Flow injection methods utilising the Karl Fischer (KF) reaction with spectrophotometric and potentiometric detection are described for the determination of the trace water content in various organic solvents. Optimisation of the methods resulted in an accessible (linear) working range of 0.01-0.2% water for many solvents studied with a typical precision of 1-2% R.S.D. Only 50 mul of organic solvent was injected and the sampling frequency was about 120 samples per h. Since the slopes of the calibration curves were different for different solvents appropriate calibration was required. Problems associated with spectrophotometric detection and caused by refractive index changes were pointed out and a nested-loop configuration was proposed to overcome this kind of interference. The potentiometric method with a novel flow-through detector cell was shown to surpass the performance of spectrophotometric detection in any respect. The characteristics of the procedures developed made them well applicable for on-line monitoring of technical solvent distillations in an industrial plant.