High-field behaviour of amorphous AsSe films

Thin films of composition AsSe_χ where 0.8 ≤ χ ≤ 1.0 obtained by the evaporation of both crystalline and glassy As₂Se₃ have been examined for their high-field behaviour. The films exhibit two essentially linear I–V regions with a smooth nonlinear change over. While the initial linear region may perhaps correspond to a Poole-Frenkel emission, the very high-field linear region is likely to arise from a distortion of the band shapes and lowering of the mobility gap.     

Computational study of buoyancy effects in a laminar starting jet

Vortical structures formed in evolving jets are important in applications such as fuel injection in diesel engines and fuel leaks. When the jet fluid is different from the ambient fluid, the buoyancy can play an important role in determining the jet flow structure, and hence, the entrainment and fluid mixing processes. In the present study, a jet of helium injected in air is investigated, with emphasis placed on delineating the buoyancy effects on vector–scalar fields during the starting phase. We utilize a computational model, previously validated to predict the flow field of low-density gas jets. The model incorporates finite volume approach to solve the transport equation of helium mass fraction coupled with conservation equations of mixture mass and momentum. Computations were performed for a laminar jet to characterize the advancing jet front, and to capture the formation and propagation of vortex rings and the related pinch-off process. Results show significant effects of buoyancy on jet advancement, as well as on vorticity and helium concentration in the core of the vortex rings.     

<Emphasis Type="Italic">P. psyllium</Emphasis>-<Emphasis Type="Italic">g</Emphasis>-polyacrylonitrile: synthesis and characterization

P. psyllium mucilage, an anionic natural polysaccharide consisting of pentosan and uronic acid obtained from the seeds of Plantago psyllium (Plantago family), was grafted with acrylonitrile (AN). Graft copolymers were prepared by grafting acrylonitrile onto P. psyllium mucilage (PSY) using ceric ion initiated solution polymerization technique for the very first time. The influence of varying concentration of (AN) and ceric ammonium nitrate (CAN) on graft copolymerization was studied. The percent grafting was found to be affected by the concentrations of AN and CAN in the reaction mixture. The prepared copolymers were not soluble in any common solvent or mixture of solvents. The prepared copolymers were characterized by FTIR.     

Reaction of water soluble polymers with oxidising agents: reaction of dextran with tetravalent cerium

Dextran, an extracellular bacterial polysaccharide, was subjected to reaction with ceric ammonium nitrate in aqueous nitric acid at varying temperatures. The polymer has been found to be degraded due to the selective oxidative cleavage of vicinal glycol units present in the monosaccharide unit of each chain. The aldehyde groups produced upon cleavage at low temperature were found to undergo further oxidation to acids and formic acid with rise in temperature of the reaction. The course of the reaction has been followed by cerimetry and by spectrophotometrical measurements. The effect of the concentration of reacting components on the reaction has been studied and various kinetic aspects have been evaluated. Depending on the kinetic results, a plausible reaction mechanism for the oxidative degradation and the subsequent reactions have been suggested by the study of the changes of solution viscosity and initiation of graft copolymerization of vinyl monomers by Ce(IV)/dextran mixture. Various thermodynamic parameters have been evaluated.     

Conjugated polymers for photocatalysis

The photocatalytic properties of the conjugated polymers have been investigated for the first time. Degradation of various textile dyes such as Alizarin S, Alizarin G, Orange G, and Remazol brilliant blue were studied under UV radiation. The experimental data indicated that the photocatalytic activity of the conjugated polymers was significantly higher than that of Degussa P-25 under similar conditions. The conjugated polymers were characterized by photoluminescent, UV-visible, and IR spectroscopies before and after photocatalytic reactions. The degradation of phenol was also carried out to study the reaction pathway of degradation.     

Rapid synthesis of ultrahigh adsorption capacity zirconia by a solution combustion technique

Tetragonal ZrO(2) was synthesized by the solution combustion technique using glycine as the fuel. The compound was characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, infrared spectroscopy, and BET surface area analysis. The ability of this compound to adsorb dyes was investigated, and the compound had a higher adsorption capacity than commercially activated carbon. Infrared spectroscopic observations were used to determine the various interactions and the groups responsible for the adsorption activity of the compound. The effects of the initial concentration of the dye, temperature, adsorbent concentration, and pH of the solution were studied. The kinetics of adsorption was described as a first-order process, and the relative magnitudes of internal and external mass transfer processes were determined. The equilibrium adsorption was also determined and modeled by a composite Langmuir-Freundlich isotherm.     

Catalytic Effect of Cetyltrimethylammonium Bromide on the Oxidation of Oxalic Acid by N-Bromophthalimide in Acidic Medium

The kinetics of micellar catalyzed oxidation of oxalic acid [OA] by N-bromophthalimide was studied in the presence of perchloric acid at 308 K. The orders of reaction with respect to [Oxalic acid], [oxidant], and [H⁺] were found to be fractional, first and negative fractional order respectively. Cationic micelles of cetyltrimethylammonium bromide increased the reaction rate. The effect of phthalimide, mercuric acetate and inorganic salts, that is, [Cl^?][Br^?] has also been done. The rate reaction decreases with increasing dielectric constant of the medium. The results are treated quantitatively in terms of Piszkiewicz and Berezin models. The rate constant (K_obs), cooperatively index (n), binding constant (k_s + k_o), and corresponding activation parameters (E_a, ΔH^#, ΔS^#, and ΔG^#) were determined. A suitable mechanism consistent with the experimental finding has been proposed.     

Acidic Peroxo Salts: A New Class of Initiators for Vinyl Polymerization. IV. Kinetics of Polymerization of Methyl Methacrylate Initiated by Potassium Monopersulfate Catalyzed by Ag(l)

Abstract

Kinetics of vinyl polymerization of methyl methacrylate (MMA) initiated by an acidic peroxo salt, such as potassium monopersulfate coupled with silver nitrate, have been investigated in aqueous medium over the temperature range from 35 to 50°C. The rates of polymerization (R_p) have been computed for various concentrations of the monomer and initiator. The effectiveness of various metal salts in catalyzing the polymerization reaction has been determined from the observed R_p values. The effects of the catalyst (AgNO₃), initiator, monomer, and various secondary aliphatic and aromatic amines on R_p and percentage conversion have been studied. The endgroups of the resultant polymers have been studied using standard methods. From the observed endgroups and kinetic results, a reaction scheme has been proposed involving initiation by ′OH or SO₄ ^? radicals, generated by the interaction of the initiator with silver nitrate and termination by mutual combination.