Heterogeneity in styrene-butadiene latex films

Low-Tg styrene-butadiene (SB) latex films were investigated by noncontact atomic force microscopy and scanning electric potential microscopy, revealing a number of different morphologies and electric potential patterns across films cast from the same SB latex dispersions under the same conditions. Surface leveling and charge dispersion throughout the films are, thus, restrained even at temperatures above Tg and the minimum film-formation temperature. An unprecedented electric pattern is observed, in which the particle cores are more positive than the contacting particle outer layers. Different packing patterns, including cubic and hexagonal arrays, coexist in neighboring areas. Zonal centrifugation of the SB latex in sucrose density gradient shows that particles cover a broad range of densities. Thus, film surface heterogeneity is at least partly due to particle heterogeneity. Fractal dimensions of topographic profiles are lower than those of the electric potential profiles, showing that charge mobility is much more restrained than polymer chain motion at the film surface and that it imposes a limit to the charged chain-ends motion.     

Selective domino ring-closing metathesis-cross-metathesis reactions between enynes and electron-deficient alkenes

[reaction: see text] A selective domino ring-closing metathesis (RCM)-cross-metathesis (CM) process between enynes and electron-deficient alkenes is reported. The conditions have been optimized for enynes 3 and methyl acrylate with catalyst IV. The scope and limitations of this reaction are described, and a possible mechanism is discussed.     

On the complexity of the Unit Commitment Problem

Annals of Operations Research - This article analyzes how the Unit Commitment Problem (UCP) complexity evolves with respect to the number n of units and T of time periods. A classical reduction...     

The effect of subcritical carbon dioxide on the dissolution of cellulose in the ionic liquid 1-ethyl-3-methylimidazolium acetate

The ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate ([emim][OAc]) readily dissolves high concentrations of cellulose. However, the high viscosity of [emim][OAc] (162 cP at 20 °C) could limit its use as a solvent for cellulose. Dissolved CO₂ has been shown to decrease the viscosity of ILs. In this study, a 50 psi CO₂ environment was applied for the dissolution of cellulose in [emim][OAc] to determine if the cellulose dissolution could be enhanced. Dissolution profiles of 4 wt% cellulose dissolved in [emim][OAc] were obtained over a 24 h period. A 75% increase in the amount of dissolved cellulose was observed with the application of a 50 psi CO₂ environment.     

Kinetic Study on Models of the Tetrabutqxyzirconium-Catalyzed Reaction Between α, ω -Dicarboxypolyamide-11 and α, ω -Dihydroxypolyoxyethylene

The kinetics of the tetrabutoxyzirconium-catalyzed esterifications between 11-dodecylamideundecanoic acid and 1-dodecanol, 2-tridecanol, a-dodecyl-ω-hydroxypolyoxyethylene are studied and compared to that of α, ω-dicarboxypolyamide-l 1 and α, ω-dihydroxypolyoxyethylene. The reaction with 2-tridecanol is characterized by an autoacceleration phenomenon. In the other cases the reaction rate is not greatly affected by catalyst concentration. An explanation involving the formation of catalyst condensates at the very beginning of the reaction is put forward.     

Diastereodivergence and appendage diversity in the multicomponent synthesis of aryl-pyrrolo-tetrahydrocarbazoles

A one-pot approach using a subsequent Cu(II)/Cu(I) catalysis and a highly diastereodivergent three-component reaction allow an easy access to various aryl-pyrrolo-tetrahydrocarbazoles with the control of up to four variable fragments and two different diastereoselectivities.     

Effect of β-cyclodextrin on spectroscopic properties of ochratoxin A in aqueous solution

Ochratoxin A (OTA) is a nephrotoxic mycotoxin produced by several fungal species, mainly Aspergillus ochraceus, A. carbonarius and Penicillium verrucosum. It contaminates many foodstuffs, particularly cereals and their derivatives, coffee, beer, wine and cocoa, and represents a serious health threat both to humans and animals. Spectroscopic properties of OTA solutions depend on the pH, solvent polarity and can be influenced by the presence of cyclodextrins (CDs). In this work, the effect of β-CD on spectroscopic properties of OTA in aqueous solutions has been investigated by means of absorption and steady-state fluorescence at different pHs (range 3.5–9.5). Binding constants of OTA/β-CD inclusion complexes have been determined by applying modified Benesi-Hildebrand equation. A 1:1 stoichiometry of OTA/β-CD complexes has been observed at all tested pHs.     

Statistique de la variable aléatoire $L(\mathit{sym}^2f,1)$

On étudie la statistique de la valeur en 1 de la fonction L de carré symétrique d'une forme primitive en calculant ses moments positifs et négatifs. On en déduit des propriétés de la répartition de ces valeurs.     

Modulation of the unpaired spin localization in Pentavalent Uranyl Complexes

The electronic structure of various complexes of pentavalent uranyl species, namely UO₂⁺, is described, using DFT methods, with the aim of understanding how the structure of the ligands may influence the localisation of the unpaired 5f electron of uranium (V) and, finally, the stability of such complexes towards oxidation. Six complexes have been inspected: [UO₂py₅]⁺ (1), [(UO₂py₅)KI₂] (2), [UO₂(salan-^tBu₂)(py)K] (3), [UO₂(salophen-^tBu₂)(thf)K] (4), [UO₂(salen-^tBu₂)(py)K] (5), [and UO₂-cyclo[6]pyrrole]^1? (6), chosen to explore various ligands. In the five first complexes, the UO₂⁺ species is well identified with the unpaired electron localized on the 5f uranium orbital. Additionally, for the salan, salen and salophen ligands, some covalent interactions have been observed, resulting from the presence of both donor and acceptor binding sites. In contrast, the last complex is best described by a UO₂²⁺ uranyl (VI) coordinated by the anionic radical cyclopyrrole, the highly delocalized π orbitals set stabilizing the radical behaviour of this ligand.