A printable optical time-temperature integrator based on shape memory in a chiral nematic polymer network

An optical and irreversible temperature sensor (e.g., a time-temperature integrator) is reported based on a mechanically embossed chiral-nematic polymer network. The polymer consists of a chemical and a physical (hydrogen-bonded) network and has a reflection band in the visible wavelength range. The sensors are produced by mechanical embossing at elevated temperatures. A relative large compressive deformation (up to 10%) is obtained inducing a shift to shorter wavelength of the reflection band (>30 nm). After embossing, a temperature sensor is obtained that exhibits an irreversible optical response. A permanent color shift to longer wavelengths (red) is observed upon heating of the polymer material to temperatures above the glass transition temperature. It is illustrated that the observed permanent color shift is related to shape memory in the polymer material. The films can be printed on a foil, thus showing that these sensors are potentially interesting as time-temperature integrators for applications in food and pharmaceutical products. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Spontaneous emission from radiative chiral nematic liquid crystals at the photonic band-gap edge: An investigation into the role of the density of photon states near resonance

In this article, we investigate the spontaneous emission properties of radiating molecules embedded in a chiral nematic liquid crystal, under the assumption that the electronic transition frequency is close to the photonic edge mode of the structure, i.e., at resonance. We take into account the transition broadening and the decay of electromagnetic field modes supported by the so-called "mirrorless"cavity. We employ the Jaynes-Cummings Hamiltonian to describe the electron interaction with the electromagnetic field, focusing on the mode with the diffracting polarization in the chiral nematic layer. As known in these structures, the density of photon states, calculated via the Wigner method, has distinct peaks on either side of the photonic band gap, which manifests itself as a considerable modification of the emission spectrum. We demonstrate that, near resonance, there are notable differences between the behavior of the density of states and the spontaneous emission profile of these structures. In addition, we examine in some detail the case of the logarithmic peak exhibited in the density of states in two-dimensional photonic structures and obtain analytic relations for the Lamb shift and the broadening of the atomic transition in the emission spectrum. The dynamical behavior of the atom-field system is described by a system of two first-order differential equations, solved using the Green's-function method and the Fourier transform. The emission spectra are then calculated and compared with experimental data. © 2013 American Physical Society.

Spontaneous emission from radiative chiral nematic liquid crystals at the photonic band-gap edge: an investigation into the role of the density of photon states near resonance.

In this article, we investigate the spontaneous emission properties of radiating molecules embedded in a chiral nematic liquid crystal, under the assumption that the electronic transition frequency is close to the photonic edge mode of the structure, i.e., at resonance. We take into account the transition broadening and the decay of electromagnetic field modes supported by the so-called "mirrorless"cavity. We employ the Jaynes-Cummings Hamiltonian to describe the electron interaction with the electromagnetic field, focusing on the mode with the diffracting polarization in the chiral nematic layer. As known in these structures, the density of photon states, calculated via the Wigner method, has distinct peaks on either side of the photonic band gap, which manifests itself as a considerable modification of the emission spectrum. We demonstrate that, near resonance, there are notable differences between the behavior of the density of states and the spontaneous emission profile of these structures. In addition, we examine in some detail the case of the logarithmic peak exhibited in the density of states in two-dimensional photonic structures and obtain analytic relations for the Lamb shift and the broadening of the atomic transition in the emission spectrum. The dynamical behavior of the atom-field system is described by a system of two first-order differential equations, solved using the Green's-function method and the Fourier transform. The emission spectra are then calculated and compared with experimental data.

Optically activated shutter using a photo-tunable short-pitch chiral nematic liquid crystal

We report the demonstration of an optically activated shutter based upon a short-pitch chiral nematic liquid crystal (LC) device sandwiched between crossed polarizers. This LC is comprised of photo-active chiral dopants. In the trans-state, the LC appears dark between crossed polarizers due to the very short pitch. As the pitch is extended through exposure to ultraviolet light, the device becomes transmissive reaching a maximum for a particular value of the pitch. As a result, it is possible to switch between the light and dark states by subjecting the device to visible light so as to cause a cis-trans photo-isomerisation. © 2013 AIP Publishing LLC.

Electrical addressing of polymer stabilized hyper-twisted chiral nematic liquid crystals with interdigitated electrodes: Experiment and model

Electro-optic switching in short-pitch polymer stabilized chiral nematic liquid crystals was studied and the relative contributions of flexoelectric and dielectric coupling were investigated: polymer stabilization was found to effectively suppress unwanted textural transitions of the chiral nematic liquid crystal and thereby enhance the electro-optical performance (high optical contrast for visible light, a near ideal optical hysteresis, fast electro-optic response). Test cells were studied that possessed interdigitated electrodes to electrically address the liquid crystal. Based on simulations, a well-fitted phenomenological description of the electro-optic response was derived considering both flexoelectro-optic and Kerr-effect based electro-optic response. © 2014 AIP Publishing LLC.

Chiral symmetry analysis and rigid rotational invariance for the lattice dynamics of single-wall carbon nanotubes

We provide a detailed expression of the vibrational potential for the lattice dynamics of single-wall carbon nanotubes (SWCNT's) satisfying the requirements of the exact rigid translational as well as rotational symmetries, which is a nontrivial generalization of the valence force model for the planar graphene sheet. With the model, the low-frequency behavior of the dispersion of the acoustic modes as well as the flexure mode can be precisely calculated. Based upon a comprehensive chiral symmetry analysis, the calculated mode frequencies (including all the Raman- and infrared-active modes), velocities of acoustic modes, and the polarization vectors are systematically fitted in terms of the chiral angle and radius, where the restrictions of various symmetry operations of SWCNT's are fulfilled.

Combined study of gamma p ->eta p and pi(-)p ->eta n in a chiral constituent quark approach

Within a chiral constituent quark model approach, η-meson production on the proton via electromagnetic and hadron probes is studied. With few parameters, the differential cross section and polarized beam asymmetry for γp → ηp and differential cross section for π − p → ηn processes are calculated and successfully compared with the data in the center-of-mass energy range from threshold up to 2 GeV. The five known resonances S11(1535), S11(1650), P13(1720),D13(1520), and F15(1680) are found to be dominant in the reaction mechanisms in both channels. Possible roles played by new resonances are also investigated; and in the photoproduction channel, significant contribution from S11 and D15 resonances, with masses around 1715 and 2090 MeV, respectively, are deduced. For the so-called missing resonances, no evidence is found within the investigated reactions. The helicity amplitudes and decay widths of N ∗ → πN, ηN are also presented and found to be consistent with the Particle Data Group values.

Study of nucleon resonances in a chiral quark model via eta productions

In this report we investigate eta-meson productions oil the proton via electromagnetic and hadron probes in a chiral quark model approach. The observables, such as, differential cross section and beam asymmetry for the two productions are calculated and compared with the experiment. The five known resonances S-11(1535) S-11(1650); P-13(1720) D-13(1520), and F-15(1680) are found to be dominant in the reaction mech-anisms in both channels. Significant, contribution from a new S-11 resonances are deduced. For the so-called "missing resonances", no evidence is found within the investigated reactions. The partial wave amplitudes for pi(-)p -> eta n are also presented.

eta photoproduction on the proton in a chiral constituent quark approach via a one-gluon-exchange model

A formalism based on a chiral quark model (chi QM) approach complemented with a one-gluon-exchange model, to take into account the breakdown of the SU(6)circle times O(3) symmetry, is presented. The configuration mixing of wave functions for nucleon and resonances are derived. With few adjustable parameters, differential cross-section and polarized-beam asymmetry for the gamma p -> eta p process are calculated and successfully compared with the data in the center-of-mass energy range from threshold to 2 GeV. The known resonances S-11(1535), S-11(1650), P-13(1720), D-13(1520), and F-15(1680), as well as two new S-11 and D-15 resonances, are found to be dominant in the reaction mechanism. Moreover, connections among the scattering amplitudes of the chi QM approach and the helicity amplitudes, as well as decay widths of resonances, are established. Possible contributions from the so-called missing resonances are investigated and found to be negligible.

Candidate chiral doublet bands in the odd-odd nucleus Cs-126

The candidate chiral doublet bands recently observed in Cs-126 have been extended to higher spins, several new linking transitions between the two partner members of the chiral doublet bands are observed, and gamma-intensities related to the chiral doublet bands are presented by analyzing the gamma-gamma coincidence data collected earlier at the NORDBALL through the Cd-116(N-14, 4n)Cs-126 reaction at a beam energy of 65 MeV. The intraband B(M1)/B(E2) and interband B(M1)(in)/B(M1)(out) ratios and the energy staggering parameter, S(I), have been deduced for these doublet bands. The results are found to be consistent with the chiral interpretation for the two structures. Furthermore, the observation of chiral doublet bands in Cs-126 together with those in Cs-124, Cs-128, Cs-130, and Cs-132 also indicates that the chiral conditions do not change rapidly with decreasing neutron number in these odd-odd Cesium isotopes.

eta production off the proton in a Regge-plus-chiral quark approach

A chiral constituent quark model approach, embodying s- and u-channel exchanges, complemented with a Reggeized treatment for the t channel is presented. A model is obtained allowing data for pi(-)p ->eta n and gamma p ->eta p to be described satisfactorily. For the latter reaction, recently released data by the CLAS and CBELSA/TAPS Collaborations in the system total energy range 1.6 less than or similar to W less than or similar to 2.8 GeV are well reproduced by the inclusion of Reggeized trajectories instead of simple. and. poles. The contribution from "missing" resonances, with masses below 2 GeV, is found to be negligible in the considered processes.

Synthesis of chiral stationary phases with radical polymerization reaction of cellulose phenylcarbamate derivatives and vinylized silica gel

Cellulose phenylcarbamate derivatives having methacrylate groups were synthesized with regioselective and non-regioselective procedures. These derivatives were chemically immobilized onto a vinylized silica gel, respectively, via a radical co-polymerization reaction. The immobilization was efficiently attained using a small amount of AIBN. The chiral recognition abilities of the prepared chiral stationary phases (CSPs) were evaluated by HPLC resolution of test enantiomers. It was observed that most of the enantiomers were completely resolved with markedly high column efficiency of 30,000-40,000 plates per metre for the eluted peaks. The effect of the amount of methacrylolyl chloride used for preparation on resolution was investigated. A direct comparison of the chiral recognition ability was made on the regioselectively and non-regioselectively prepared CSPs. In addition, the chemically bonded-type of CSPs were found to be relatively stable with addition of solvents such as tetrahydrofuran (THF) and chloroform into the mobile phase, which can lead to the dissolution of cellulose derivatives on the coated CSPs. Thus the choice of solvents used as the mobile phase is greatly extended and better resolution of several test enantiomers was observed on the prepared CSPs with THF and chloroform as a composition in the mobile phase. The batch-to-batch and run-to-run reproducibility was also discussed on the newly prepared CSPs. (C) 2004 Elsevier B.V. All rights reserved.

New chiral ferrocenyldiphosphine ligand for catalytic asymmetric transfer hydrogenation

New chiral ferrocenyldiphosphine ligands (R)-(S)-3 and (R)-(S)-4 were prepared. The ligands were employed in Ru(II) catalyzed asymmetric transfer hydrogenation of ketones to give corresponding secondary alcohols. Up to 99% conversion with 90% e.e. was obtained on Ru(DMSO)(4)Cl-2/4 in transfer hydrogenation of acetophenones with propan-2-ol. (C) 2003 Elsevier B.V. All rights reserved.