New polymorphs of alumina

Abstract

We present the results of high-pressure, high-temperature studies on xerogel gamma alumina which is made up of nanocrystalline alumina and an amorphous phase. Not many studies of this type have been reported on xerogel materials. At about 5 GPa and 1400°C, the xerogel alumina transforms into a polymorphic mixture containing α Al₂O₃, B Al₂O₃ and C Al₂O₃ where the last two phases have B Ln₂O₃ and C Ln₂O₃ type structures respectively. Here Ln stands for the rare earths. The xerogel alumina containing 1 wt.% Cr₂O₃ under these conditions transforms into a polymorphic mixture containing Al₂O₃, k' Al₂O₃ and H Al₂O₃ where H Al₂O₃ has the H Ln₂O₃ type structure. For the first time, the observation of rare earth sesquioxide structures of alumina is reported. At about 5 GPa at 27°C, the xerogel aluminal transforms to an amorphous phase. The results are discussed using the free energy diagram for xerogels proposed by R. Roy (J. Amer. Cer. Soc., 52, 344, 1969; 67, 468, 1984).     

Use of polystyrene brushes to investigate the role of interface between substrates and thin homogeneous films

The viscoelastic properties of thin polystyrene (PS) films depend on confinement, as it can modify the molecular dynamics affecting the glass transition. In the recent past, the authors have investigated the region next to the free interface by means of an atomic force microscope suitably modified to monitor the indentation of a tip into a film during a given lapse of time while applying a constant load. Herein, to explore the interface with the substrate, the authors report on experiments in which PS brushes grafted to native silicon oxide were used. It was found that the film wettability on brushes and H‐terminated silicon can be highly improved when compared with native silicon oxide. In addition, the glass transition temperature of thin films increases up to the bulk value in the case of film/brush combinations with high molecular weight or films with high molecular weight on H‐terminated silicon. Data are discussed according to hypotheses such as residual solvent presence, interface free volume, and molecular mechanical coupling. These observations can be of great interest for nanotechnological applications, especially in those instances where one needs to tailor the temperature dependence of viscoelastic properties of thin films. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1149–1156     

Efficient and strategy-proof social choice when preferences are single-dipped

We study the problem of locating a single public good along a segment when agents have single-dipped preferences. We ask whether there are unanimous and strategy-proof rules for this model. The answer is positive and we characterize all such rules. We generalize our model to allow the set of alternatives to be unbounded. If the set of alternatives does not have a maximal and a minimal element, there is no meaningful notion of efficiency. However, we show that the range of every strategy-proof rule has a maximal and a minimal element. We then characterize all strategy-proof rules.     

Structural Characterization of Composite Particles of Two Commonly Used Herbicides

A spray drying technique was applied to prepare composite microparticles of a water-insoluble herbicide, atrazine(AT) and a water-soluble herbicide 2,4-dichloro phenoxy acetic acid (2,4-D) for the purpose of improving the water solubility of AT. A homogenous mixture of an ethanol solution of AT and an aqueous 2,4-D solution at different ratios were spray dried using a laboratory scale spray drier. Quantitative elemental analysis suggested that the AT/2,4-D ratio in each composite microparticle was nearly the same as the desired formulation ratio. The resulting samples were characterized by powder x-ray diffractometry (XRD), differential scanning calorimetry (DSC), Fourier transform infra red (FT-IR) and scanning electron microscopy (SEM). It was found that the crystallinity of AT and 2,4-D were maintained in the composite particles. Moreover, the release of AT from dissolved composite microparticles was markedly improved because of an increase in the effective surface area following rapid dissolution of 2, 4 D. Hence, this study shows that it is possible to prepare AT-2,4-D composite microparticles using a laboratory scale spray drier and that this can improve the ability of AT to dissolve in water.     

2-O-Benzylation in D-Gluconamide Derivative Under Basic Conditions with Complete Retention of Stereo-Integrity: Convenient Access to 2-O-benzyl-3,4:5,6- di-O-isopropylidene-D-glucitol and other Differently Protected D-glucitol Derivatives

A new and convenient synthesis of 2-O-benzyl-3, 4: 5, 6-di-O-isopropylidene-D-glucitol has been accomplished and has been generalized with the syntheses of differently protected D-glucitols at C-2 position. In the course of our new route to the differently protected D-glucitols at C-2 position, a new D-gluco configured building block, 1-morpholino-(3, 4: 5, 6-di-O-isopropylidene)-D-gluconamide has been achieved.     

Biotinylated Poly(3-Hexylthiophene-co-3-Methanolthiophene): A Langmuir Monolayer-Forming Copolymer

Abstract

Copolymers of 3-substituted thiophenes have been synthesized by organosynthetic routes. The chemical synthesis of the copolymer was carried out by dehydrogenation of 3-hexylthiophene and 3-methanolthiophene. Attachment of biotin to the resulting copolymer, poly(3-hexylthiophene-co-3-methanolthiophene) [PMHT], is accomplished by room temperature esterification using N,N-dicyclohexylcarbodiimide (DCC) and 4-pyrrolidinopyridine as catalyst. The resulting copolymers have well-defined chemical and electronic structures and molecular weights. The biotinylated copolymer forms a stable monolayer at the air-water interface due to the polar groups along the polymer backbone.     

Effect of chlorine on the adsorption of oxygen on Cu and Ag surfaces

Based on XPS and UVPS studies, it is shown that oxygen is preferentially adsorbed molecularly in the singlet state on Cu and Ag surfaces containing presorbed chlorine. Adsorption of chlorine on Cu and Ag surfaces containing presorbed atomic oxygen causes a disappearance of the oxygen. Extended Hückel calculations predict the observed behaviour.