Thermally stable holographic surface relief gratings and switchable optical anisotropy in films of an azobenzene-containing polyelectrolyte

In a search for effective polymer film material for holographic surface patterning, commercially available azobenzene polyelectrolyte has been employed. Films of good optical quality in a wide range of thickness were produced. Optical dichroism up to 0.19 was induced upon irradiation with linearly polarized light. Surface relief gratings with amplitudes up to 630 nm and diffraction efficiency of 37% were inscribed by holographic exposure to the light of 488 nm. Due to the ionic nature of the material, the relief was stable at least up to the temperature of decomposition (ca. 200 degrees C) but could be erased and inscribed again by light.     

Morphology and switching of holographic gratings containing an azo dye

The effects of an azo dye on the diffraction efficiency, morphology and electro-optic properties of the transmission mode of a holographic polymer dispersed liquid crystal (LC) have been studied. The azo dye induced an induction period which otherwise does not exist, followed by a gradual increase of the diffraction efficiency to a saturation value which increased with increasing azo dye content, as a result of the azo dye reorientating LC molecules within the droplet. The increased diffraction efficiency was caused by the decreased droplet coalescence which was due to the hindered migration of the LC by the dye molecules, and to LC orientation induced by azo dye molecules giving a high refractive index contrast. The droplet size decreased with increasing dye content. The dye also lowered the threshold voltage due to the high dielectric anisotropy caused by the presence of a strong on-axis dipole moment and decreased the response time.     

Electrooptical properties of polarization holographic gratings formed in liquid-crystal composites

The results of experimental study of the electrooptical properties of polarization holographic gratings formed in a liquid-crystal composite by polarization holography are presented. The influence of the formation conditions, the parameters of the controlling ac electric field, and the composite geometry on the diffraction efficiency of such gratings is considered.     

Molecular weight effect on the photoinduced birefringence and surface relief gratings formation of a methacrylate azopolymer

Samples of a methacrylic side-chain azopolymer were synthesized by a radical copolymerization of methyl-methacrylate with the methacrylic derivative of the commercial dye Disperse Red-13 (DR13). Copolymers with different molecular weight were obtained by varying the reaction time and the concentration of initiator. Samples with molecular weight averages (M_w) from 3 to 8 × 10⁴ g/mol and 1.4-1.7 polydispersity were obtained. The glass transition temperature of the samples increased linearly from the lower to the highest molecular weight. Optical quality cast films were prepared for all samples and photoinduced birefringence was successfully carried out in all samples as well as surface relief gratings could be inscribed in the cast films.     

Time-resolved high-performance liquid chromatography fluorescence detector using a nanosecond pulsed light source for detecting lanthanide-chelated compounds

We have constructed a time-resolved fluorescence detection (TRFD) system for the analysis of amino compounds with high-performance liquid chromatography (HPLC) using lanthanide ion chelates. In order to carry out time-resolved measurements, we have employed a nanosecond pulsed xenon-arc lamp as an excitation light source. Amino compounds derivatized by isothiocyanobenzyl-EDTA (IEDTA) with the lanthanide chelate are mixed with an enhancer solution in a post-column manner and detected by TRFD. Taking advantage of a property of the long fluorescence lifetime of the lanthanide chelates, high selectivity against background fluorescence was achieved. In order to demonstrate the usefulness of TRFD, fundamental performance tests were carried out. Details of the system are also described.     

Comparative study of holographic recording in cholesteric and nematic azo-containing side-chain polymers

For the first time a comparative study of holographic recording in planarly oriented films of nematic and cholesteric azobenzene-containing polymers was performed. The influence of temperature and light intensity on the values of diffraction efficiencies of holographic gratings was investigated. The kinetics of grating relaxation at different temperatures was studied. It was shown that the helical supramolecular structure of cholesteric copolymer causes a significant decrease of the diffraction efficiency in comparison with the one observed for the nematic state of the homopolymer.     

On the scattering of a light pulse on a single atom perturbed by collisions with inert gas atoms

The excitation of the strontium-like systemS ₀ —P ₁ by the light pulse of duration comparable or larger than relaxation times is considered. The influence of the different pulse envelopes on the time evolution of the density matrix components and on energy spectrum is analyzed. In the case of large detuning and small Rabi frequency the secular approximation is adopted.     

Formation of an intermediate radical cation in the nanosecond pulse radiolysis of Malachite Green Leucocyanide in organic solvents

The malachite green leucocyanide (MGCN) was irradiated in argon or oxygen saturated solutions of n-butyl chloride, 1.2-DCE, CCl₄ and acetone with 13 ns electron pulses. Two species with absorption maxima at 620 and 480 nm were observed. The latter was attributed to the malachite green leucocyanide radical cation (MGCN^+.) and the former to the known carbonium ion of malachite green dye (MG⁺). Observation of the consecutive charge transfer via the schemes: DCE^+. → BPh^+. → MGCN^+. and DCE^+. → MGCN^+. → TMPD^+., allowed to estimate the ionization potential of MGCN molecule in the range 6.9 eV < Ip_MGCN < 8.27 eV. Presented results and literature data suggest that positive charge in MGCN^+. radical cation is located in the “aniline” part of the molecule.     

On the scattering of a light pulse on a single atom perturbed by collisions with inert gas atoms

Scattering of a laser pulse on a single atom perturbed by collisions with inert gas atoms is described in terms of suitably defined cross-sections. The relations of the energy balance are explored to show the connection between attenuation and total cross-section for scattering. The different scattering channels, corresponding to the polarisation, spectral decomposition and coherence properties of the light are analysed in terms of the cross-sections. As an example we consider the scattering of a light pulse on an alkali metal atom with a frequency close to the atomic transition frequency from the ground stateS _1/2 to the first excited stateP _1/2.     

The direct observation of a highly mobile positive ion in nanosecond pulse irradiated liquid cyclohexane

The electrical conductivity induced by pulse irradiation of liquid cyclohexane has been studied by means of microwave absorption. The conductivity in pure cyclohexane, due principally to the excess electron, is reduced to less than 10% of the initial value on addition of 5 × 10^?4 M of the electron scavenger SF₆. The conductivity remaining after addition of SF₆ is however more than an order of magnitude larger than expected for massive ions in cyclohexane and, since it is almost completely removed by the addition of 4 × 10^?3 M of the positive ion scavenger NH₃, is attributed mainly to the high mobility of the positive hole in this liquid. The ratio of the electron to hole mobility is determined to be 15. The mean lifetime of the hole under the present conditions is 86 ns. The rate constant for reaction of the hole with NH₃ is determined to be 1.8 × 10¹¹ M^?1 s^?1. From the conductivity remaining after removal of both the electron and the hole the sum of the mobilities of the resulting molecular ions is determined to be 8.4 × 10^?4 cm² V^?1 s^?1.     

Fast analysis of drugs in a single hair

A new method for the fast screening of cocaine and 6-monoacetylmorphine (6-MAM) in a single hair, using gas chromatography/mass spectrometry (GC/MS), is described. The analyses are conducted in less than 10 min with minimal sample preparation. The novel method combines the ChromatoProbe direct sample introduction device for intrainjector thermal extraction, fast GC separation, a supersonic molecular beam GC/MS interface and hyperthermal surface ionization (HSI). The technique has been successfully employed for the detection of cocaine in as little as a 1-mm section of hair using selected ion monitoring (SIM). Unambiguous full scan mass spectra of cocaine and 6-MAM were obtained on a single hair for cocaine and heroin users, respectively. HSI was found to be almost 3 orders of magnitude more selective than electron impact ionization for cocaine compared with the major hair constituents, with a minimum detected concentration of approximately 10 ppb in the SIM mode. Results obtained for 12 drug users showed full qualitative agreement with similar results using rigorous solvent extraction followed by electrospray-liquid chromatography/mass spectrometry analysis. However, quantitative studies showed only partial agreement. No false positives were observed for 10 drug free subjects. This method enables fast drug monitoring along the hair length which permits time correlation studies.     

Fast self-propagating chemical processes in inorganic solids induced by an elastic wave pulse

Fast self-propagating chemical processes in solids initiated by an elastic wave pulse were studied in relation to ammonium dichromate. A possible mechanism for these processes was proposed. Dedicated to the memory of Academician M. E. Vol'pin timed to his 75th birthday. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1140–1144, June, 1998.     

Identification of a single light atom within a multinuclear metal cluster using valence-to-core X-ray emission spectroscopy

Iron valence-to-core Fe Kβ X-ray emission spectroscopy (V2C XES) is established as a means to identify light atoms (C, N, O) within complex multimetallic frameworks. The ability to distinguish light atoms, particularly in the presence of heavier atoms, is a well-known limitation of both crystallography and EXAFS. Using the sensitivity of V2C XES to the ionization potential of the bound ligand, energetic shifts of ~10 eV in the ligand 2s ionization energies of bound C, N, and O may be observed. As V2C XES is a high-energy X-ray method, it is readily applicable to samples in any physical form. This method thus has great potential for application to multimetallic inorganic frameworks involved in both small molecule storage and activation.     

Optical dating of archaeological samples using a single aliquot of quartz stimulated by blue light

The single aliquot additive dose method of equivalent dose determination was applied to quartz from heated archaeological materials, using luminescence stimulated by blue light. The quartz was extracted from pieces of pottery and kiln in an area of archaeological interest in Suwon region, south of Seoul, Korea. The dates obtained were in good agreement with the ages derived by archaeological evidence. It is concluded that the additive dose single aliquot method of determining equivalent dose, with correction for re-use of the aliquot, should contribute significantly to optically stimulated luminescence dating procedures, particularly when the amount of sample separated is limited. Additionally, some luminescence images from quartz samples using a CCD camera are presented and relationships between AGTL, TL and OSL are discussed.     

Observation of an inefficient photocyclization with a holographic method

The holographic photochemical signal from triphenylimidazole in a polyvinylbutyral film, using the ultraviolet lines of an argon ion laser arises from its cyclization to 2-phenyl-9,10-phenanthroimidazole. An irreversible ultraviolet active holographic photochemical system is illustrated for which the final photoproduct appears to be stable.     

Mechanically compliant single crystals of a stable organic radical

Mechanically compliant organic crystals are the foundation of the development of future flexible, light-weight single-crystal electronics, and this requires reversibly deformable crystalline organic materials with permanent magnetism. Here, we report and characterize the first instance of a plastically bendable single crystal of a permanent organic radical, 4-(4′-cyano-2′,3′,4′,5′-tetrafluorophenyl)-1,2,3,5-dithiadiazolyl. The weak interactions between the radicals render single crystals of the β phase of this material exceedingly soft, and the S–N interactions facilitate plastic bending. EPR imaging of a bent single crystal reveals the effect of deformation on the three-dimensional spin density of the crystal. The unusual mechanical compliance of this material opens prospects for exploration into flexible crystals of other stable organic radicals towards the development of flexible light-weight organic magnetoresistance devices based on weak, non-hydrogen-bonded interactions in molecular crystals.

Mechanically soft crystals are interesting candidates for single crystal electronics. Here, crystals of a stable dithiadiazolyl radical are shown to be plastically bendable and display a change in their spin density in response to mechanical force.     

Measurement of long-range forces on a single yeast cell using a gradient optical trap and evanescent wave light scattering

The long-range equilibrium and viscous interaction forces between a single Candida albicans cell and a flat surface have been measured using a gradient optical trap as a force transducer and evanescent wave light scattering (EWLS) to determine the separation distance. In this technique the trapped cell is probed against the surface by moving the focal point of the optical trap, the equilibrium force is determined by the deflection of the most probable cell position from the trap center, and the viscous forces are determined from the relaxation time of the Brownian fluctuations of the cell in the trap. At low electrolyte concentrations (0.5 mM NaCl) where double layer repulsion was anticipated to be the dominant interaction, equilibrium force–distance profiles for yeast cells and similarly sized polystyrene microspheres on glass surfaces both showed good agreement with predictions of DLVO theory. Also, viscous drag profiles at larger separation distances where interaction forces were small agreed well with Stokes flow predictions. These results appear to validate the technique for use with spherical yeast cells and other bioparticles of similar size. This force measurement methodology therefore provides a complementary alternative to atomic force microscopy for direct force measurement with much greater sensitivity for studying interaction between yeast and surfaces.     

Geographical traceability of wheat and its products using multielement light stable isotopes coupled with chemometrics

The present study was aimed to investigate the variation of stable isotopic ratios of carbon, nitrogen, hydrogen, and oxygen in wheat kernel along with different processed fractions from three geographical origins across 5 years using isotope ratio mass spectrometry (IRMS). Multiway ANOVA revealed significant differences among region, harvest year, processing, and their interactions for all isotopes. The region contributed the major variability in the δ¹³C ‰, δ²H ‰, δ¹⁵N ‰, and δ¹⁸O‰ values of wheat. Variation of δ¹³C ‰, δ¹⁵N ‰, and δ¹⁸O ‰ between wheat whole kernel and its products (break, reduction, noodles, and cooked noodles) were ?0.7‰, and no significant difference was observed, suggesting the reliability of these isotope fingerprints in geographical traceability of wheat‐processed fractions and foods. A significant influence of wheat processing was observed for δ²H values. By applying linear discriminant analysis (LDA) to the whole dataset, the generated model correctly classified over 91% of the samples according to the geographical origin. The application of these parameters will assist in the development of an analytical control procedure that can be utilized to control the mislabeling regarding geographical origin of wheat kernel and its products.