Kinetics of grafting acrylonitrile onto starch

Acrylonitrile (AN) was graft copolymerized onto gelatinized and granular wheat starch in aqueous media in the presence of ceric ammonium nitrate initiator at 91-364 anhydroglucose units (AGU) per cerium (IV) and at 1.08-4.33 AN to AGU ratios. Molecular weights and dispersities of polyacrylonitrile side chains were determined by gel-permeation chromatography. Conversion-time plots of AN polymerizations in both gelatinized and granular starch systems show characteristics common to heterogeneous polymerizations that could be explained on the basis of buried polymer radicals. The rates of polymerizations were directly related to the square root of the corrected cerium(IV) concentration and to the 1.3 power of the AN concentration. Graft copolymerization of AN onto starch, at least during initial stages, is not suitably explained by a kinetic scheme involving termination by polymer radical with cerium(IV) ion.     

Membership

Abstract

Stanford Resources Inc., the leading market research firm specializing in the global electronic display industry, has released its annual study on the flat panel display (FPD) industry - Flat lnformation Displays. Now in its eighth edition, this industry perspective analyses competing FPD technologies in terms of technological development, sales, suppliers and future prospects.     

Dielectric relaxation of water molecules in different lyotropic structures of nonylphenoxypoly(ethylenoxy)ethanol (Ark. 9)

Abstract

Dielectric relaxation of water molecules in the lamellar, L_α, cubic and hexagonal, H_α, lyotropic structures of nonylphenoxy-poly(ethylenoxy)ethanol (Ark. 9) has been studied by dielectric time domain spectroscopy in the frequency range between 10 MHz and 10 GHz. The values of the relaxation times, obtained at room temperature, are the following: 41 ps for the L_α phase, 29 ps for the cubic phase and 22 ps for the H_α phase. As is seen, the relaxation time of bound water is distinctly higher than that of pure water, and it depends strongly on the phase structure. The relaxation times measured for the liquid-crystalline phases as well as for pure Ark. 9 obey the Arrhenius law, and the energy barriers obtained have the following values: (20 ± 2) kJ/mol for all the liquid-crystalline phases, and (30 ± 3) kJ/mol for pure Ark. 9. The former is in good agreement with the value found for bound water in lipid systems whereas the latter is characteristic of the isotropic phase of thermotropic liquid crystals.     

Analysis of Malathion and its Breakdown Products in Aquaria Containing Golden Shiners (N. CHRYSOLEUCAS)

Abstract

The 1-ethylmonocarboxylic acid of Malathion (MCA) was identified as a metabolite of Malathion in the gut of golden shiners (N. Chrysoleucas) (7.11 × 10²±0.66 × 10² ng/g tissue). As noted in the literature the rate of hydrolysis of Malathion above pH 7 is first order with respect to Malathion and pH dependent. In addition, the rate of hydrolysis of Malathion in aquaria housing these fish was found to be dependent on the concentration of Ca⁺²; sparging the aquaria with air affected the rate. Some of the hydrolysis products of Malathion were identified by gc/ms and found to be pH dependent above pH 7. The half-life of Malathion under different conditions, the identification of some hydrolytic products and a general scheme for the analysis of Malathion, along with some of its metabolic and hydrolytic products are included in this paper.     

Photophysics of Silicon Phthalocyanines in Aqueous Media

Phthalocyanines have been used as photodynamic therapy (PDT) agents because of their uniquely favorable optical properties and high photostability. They have been shown to be highly successful for the treatment of cancer through efficient singlet‐oxygen (¹O₂) production. However, due to their hydrophobic properties, the considerations of solubility and cellular location have made understanding their photophysics in vitro and in vivo difficult. Indeed, many quantitative assessments of PDT reagents are undertaken in purely organic solvents, presenting challenges for interpreting observations during practical application in vivo. With steady‐state and time‐resolved laser spectroscopy, we show that for axial ligated silicon phthalocyanines in aqueous media, both the water:lipophile ratio and the pH have drastic effects on their photophysics, and ultimately dictate their functionality as PDT drugs. We suggest that considering the presented photophysics for PDT drugs in aqueous solutions leads to guidelines for a next generation of even more potent PDT agents.     

Response times and voltages for PDLC light shutters

The response times and operating voltages of light shutters formed from polymer dispersed liquid crystals (PDLCs) have been studied experimentally and the results compared with calculations based on non-sperhically shaped nematic droplet models. The experiments were performed on light shutters with elongated and uniformly aligned droplets where the relaxation time and voltage response were measured. It is shown that the droplet shape can be a dominant factor, particularly for the relaxation time, and the data are compared with equations derived in terms of the aspect ratio of the droplet l = a/b, where a and b are the lengths of the semi-major and semi-minor axes, respectively, of the elongated droplet. It is further demonstrated that the electric field inside the droplet can be considerably smaller than the applied field, due to the conductivity and dielectric properties of the polymer and liquid crystal materials. These data are used to obtain values for the ratio of the conductivities of the polymer binder and liquid crystal droplet, as well as the anisotropy of the conductivity in the liquid crystal.     

Polymer modified and stabilized cholesteric liquid crystal materials for flat panel application

Polymer dispersions, even in very low concentrations, can improve the performance of cholesteric liquid crystal materials necessary for their application in flat panel displays. Normal scattering mode, reverse scattering mode and reflective mode cholesteric liquid crystal materials are described. The roll of the polymer in each of these display modes is reviewed as are the unique electro-optic characteristics of the dispersions.     

Twist impeded self-diffusion in a cholesteric

Molecular self-diffusion along the pitch axis of a twisted nematic is measured by its motional averaging effect on the deuterium quadrupole interaction. The diffusion constant is found to decrease as the pitch length is decreased. This result is explained by simple phenomenological considerations and is consistent with published viscosity measurements.