GREEN’S FUNCTION AND EFFECTIVE ELASTIC STIFFNESS TENSOR FOR ARBITRARY AGGREGATES OF CUBIC CRYSTALS

A closed but approximate formula of Green’s function for an arbitrary aggregate of cubic crystallites is given to derive the e?ective elastic sti?ness tensor of the polycrystal. This formula, which includes three elastic constants of single cubic c…     

Photorefractive Four-Wave Mixing Switches Utilizing Pockels Effect -Longitudinal and Lateral Switches-

We carried out detailed calculations for photorefractive wave-mixing switches based on one of three crystals with high electro-optic coefficients, namely, BaTiO₃, Strontium Barium Niobate (SBN (0.75)), and Potasium Sodium Strontium Barium Niobate (KNSBN). A comparison of results for the three crystals shows that a 0_-cut BaTiO³ crystal is suitable for a longitudinal switch and requires a voltage of about 80 for a 2-mm-thick crystal to induce sufficient phase mismatch. The electrodes must be transparent for the incident and diffracted beams. A 45_-cut SBN (0.75) crystal, however, is suitable for a lateral switch and requires a voltage of about 150 for a 1-mm-wide crystal. The electrodes do not need to be transparent.     

Color Zone Map in Peripheral Vision at Various Illuminance Levels

We measured the entire region of mesopic and photopic vision to determine the color zone covering the visual field with unique red, yellow, green, and blue hue components. Eight kinds of test stimuli in the natural color system (NCS) color notation system were used. These stimuli were presented at horizontal and vertical meridians, and at meridians inclined at 45° angles. The illuminance level was set at six levels: 0.01 lx-1000 lx. The evaluation method measured chromatic, white, and black components as well as the hue component of the stimuli. Results show that the color zone of the retina extended further into the periphery with increasing illuminance; the response of opponent colors y-b was shown to be greater than that of the opponent colors r-g.     

Real-time color holographic interferometry devoted to 2D unsteady wake flows

A new optical technique based on real time holographic interferometry in true colors has been implemented around the transonic wind tunnel of the ONERA-Lille center to analyze 2D unsteady wake flows. Tests realized in color interferometry, real time and double exposure, use simultaneously three wavelengths of a continuous waves laser (argon and krypton mixed) and holograms are recorded on silver-halide single-layer panchromatic Slavich PFG03c plates. The very principle of real-time true color holographic interferometry uses three primary wavelengths (red, green and blue) to record, under no-flow conditions, the interference among the three measurement beams and the three reference beams simultaneously on a single reference hologram. After the holographic plate is developed, it is placed on the test setup again in the position it occupied during exposure and the hologram is illuminated again by the three reference beams and three measurement beams. A flat, uniform color can then be observed behind the hologram. So a horizontal, vertical, or even circular fringe pattern can be formed and the achromatic central fringe can be made out very clearly. The single color is used to determine the path difference zero on the interferograms. The flow studied was the unsteady flow downstream of a cylinder placed crosswise in the test section. A sequence of hundred interferograms was recorded on the flow around the cylinder at Mach 0.37. The vortex formation and dissipation phases can be seen very clearly, along with the fringe beat to either side of the cylinder.     

Synthesis of a soluble pyrrole copolymer with phenetidine

A new series of copolymers was synthesized through the oxidative polymerization of pyrrole (PY) and o‐phenetidine (PHT) with inorganic oxidants in acidic media. The polymerization parameters including the mixing method of the oxidant with the comonomer, the comonomer ratio, the time, the temperature, the oxidant, the organic medium, and the acid were systematically optimized for the synthesis of copolymers with high yields, intrinsic viscosities, and solubility. The resultant copolymers were characterized by elemental analysis, infrared, ultraviolet–visible, solution high‐resolution ¹H NMR and solid‐state high‐resolution ¹³C NMR, circular dichroism spectroscopy, and cyclic voltammetry. The results showed that the PY observed content in the copolymers was much higher than the PY feed content. The regular variation of the polymerization yield, intrinsic viscosity, solubility, macromolecular structure, and electroactivity of the resulting polymers with the comonomer ratio, together with the complete solubility of a PY/PHT (10/90) polymer in highly polar solvents, indicated the formation of real random copolymers containing both PY and PHT units rather than a mixture of two homopolymers. However, the polymers containing more than 59 mol % PY were not homogeneous copolymers consisting of soluble and insoluble parts. A semiquantitative relationship between the polymerization yield or solubility of the copolymers and the polarity index of the organic solvents was examined. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2073–2092, 2004     

Living polymerization of styrene initiated by mercaptan/ε‐caprolactam

The bulk polymerization of styrene initiated by ?‐caprolactam (CL) and n‐dodecyl mercaptan (RSH) has been explored. This novel polymerization system shows living characteristics. For example, the molecular weight of the resulting polymers increases with conversion, and the system has the ability to form diblock copolymers and so forth. The polymer chain end contains thiol and lactam structures, which we have investigated with Fourier transform infrared, ¹H NMR, and ¹³C NMR techniques. Electron spin resonance spectra and theoretical calculations by the Hartree–Fock methods have been used to examine the mechanism. The results reveal that the initial polymerization starts from thiol via a chain‐transfer reaction, and the propagation proceeds by the insertion of a monomer between the terminal group and the intermediate structure of lactam. Finally, the polymerization kinetics have been examined. The polymerization rate varies linearly with the concentration of CL and RSH, and this confirms the mechanism. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4976–4993, 2004     

Synthesis and characterization of new segmented polyurethanes with side‐chain,liquid‐crystalline chain extenders

Liquid‐crystalline, segmented polyurethanes with methoxy–biphenyl mesogens pendant on the chain extender were synthesized by the conventional prepolymer technique and esterification reaction. Two, side‐chain, liquid‐crystalline (SCLC) polyurethanes with mesogens having spacers of six and eight methylene units were prepared. The structures of the mesogenic units and SCLC polyurethanes were confirmed by Fourier transform infrared spectroscopy and ¹H NMR. Polymer properties were also examined by solubility tests, water uptakes, and inherent viscosity measurements. Differential scanning calorimetry studies indicated that the transition temperature of the isotropic to the liquid‐crystalline phase decreased with increasing spacer length. Wide‐angle X‐ray diffraction (WAXD) studies revealed the existence of liquid‐crystalline phases for both SCLC polyurethanes. Polarized optical microscopic investigations further confirmed the thermotropic liquid‐crystalline behaviors and nematic mesophases of both samples. Thermogravimetric analysis displayed better thermal stabilities for both SCLC polymers and indicated that the presence of mesogenic side chains may increase the thermal stability of segmented polyurethanes. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 290–302, 2004     

Behavior and surface energies of polybenzoxazines formed by polymerization with argon,oxygen, and hydrogen plasmas

Polybenzoxazine (PBZZ) thin films can be fabricated by the plasma‐polymerization technique with, as the energy source, plasmas of argon, oxygen, or hydrogen atoms and ions. When benzoxazine (BZZ) films are polymerized through the use of high‐energy argon atoms, electronegative oxygen atoms, or excited hydrogen atoms, the PBZZ films that form possess different properties and morphologies in their surfaces. High‐energy argon atoms provide a thermodynamic factor to initiate the ring‐opening polymerization of BZZ and result in the polymer surface having a grid‐like structure. The ring‐opening polymerization of the BZZ film that is initiated by cationic species such as oxygen atoms in plasma, is propagated around nodule structures to form the PBZZ. The excited hydrogen atom plasma initiates both polymerization and decomposition reactions simultaneously in the BZZ film and results in the formation of a porous structure on the PBZZ surface. We evaluated the surface energies of the PBZZ films polymerized by the action of these three plasmas by measuring the contact angles of diiodomethane and water droplets. The surface roughness of the films range from 0.5 to 26 nm, depending on the type of carrier gas and the plasma‐polymerization time. By estimating changes in thickness, we found that the PBZZ film synthesized by the oxygen plasma‐polymerization process undergoes the slowest rate of etching in CF₄ plasma. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4063–4074, 2004     

Viscosity,particle size distribution,and structural investigation of tetramethyloxysilane/2‐hydroxyethyl methacrylate sols during the sol–gel process with acid and base catalysts

The tetramethoxysilane (TMOS)/2‐hydroxylethyl methacrylate (HEMA) hybrid gels were synthesized with acid and base catalysts, via the in situ polymerization of HEMA, with and without the cosolvent methanol. With methanol in the TMOS/HEMA sol, the enhanced esterification and depolymerization reactions of the silanols resulted in a slower growth of silica particles. The silica particles that were synthesized with an acid catalyst were less than 40 nm. The thermal resistance of the poly(2‐hydroxyethyl methacrylate) (PHEMA) chains was enhanced by the addition of colloidal silica. The Fourier transform infrared characterizations and the exothermal peaks on the differential scanning calorimetry traces of these hybrid gels indicated chemical hybridization occurring as a result of condensation of the colloid silica and PHEMA at higher temperatures. Hence, the residual weight content of the hybrid gel after its synthesis with the base catalyst was even higher than the content of TMOS in the hybrid sol. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3476–3486, 2004     

Determination of polymeric aluminum in soil extracted with a modified anion-exchange resin as a solid-phase adsorbent by ICP-AES.

In the present work, a new method was established by applying solid-phase extraction (SPE) to preconcentrate and separate polymeric aluminum (Al) and using ICP-AES to determine the polymeric Al, the total monomeric Al, and the total Al in soil extracts, respectively. A modified resin was prepared with impregnated 8-hydroxyquinoline-5-sulfoxinate (HQS) on the anion-exchange resin. It has good recognition ability for Al fractions, compared to the commonly used cation ion-exchange resin, which has a better ability to adsorb cations and a weak ability to recognize detailed Al species. The optimum conditions for Al fractionation sorption, elution and separation and the interference of foreign ions were studied with the prepared resin by continuous column and batch procedures. Monomeric Al was bound to Pyrocathecol Violet (PCV) at pH 6.2, whereas the polymeric Al species did not react with PCV for at least 15 min. Because a stable complex of Al-PCV was not absorbed on the HQS modified resin, the polymeric Al could be preconcentrated on-line by the HQS-modified resin. The adsorbed polymeric Al was eluted with 3 mL of 3 mol L(-1) of HCl, and then detected by ICP-AES. The method has been applied to directly determine polymeric Al in soil extracts with high selectivity as well as a high preconcentration factor. It gives a limit of detection of 0.6 ng mL(-1) with a relative standard deviation of less than 5.7% (n = 5, 0.24 microg mL(-1) Al).