Synthesis,characterization and optical properties of graphene oxide–polystyrene nanocomposites

The synthesis of graphene oxide (GO)–polystyrene (PS) Pickering emulsions, as environment‐friendly nanostructures suitable for novel applications, has received significant attention in recent years. In this work, the synthesis and characterization of GO–PS nanocomposites through seeded emulsion polymerization and the selective light reflection properties of dry films have been reported. Amphiphilic molecule sulfonated 3‐pentadecyl phenol was used as a co‐surfactant to stabilize GO dispersions during the emulsion polymerization process. The particle size of the dispersions as measured by dynamic light scattering decreases from 540 nm, for PS without any GO, to 88 nm with 1 wt% GO content. Scanning electron microscopy studies show a uniform size distribution of the composite particles prepared with GO. The dried films show a structural color that varies with the GO content. The self‐assembly behavior of the dried film was further studied using reflectance spectroscopy, which shows a red shift of the reflectance maximum from 440 to 538 nm as the GO loading was increased from 0.2 to 0.5 wt%, respectively, indicating a different microstructure. X‐ray diffraction, transmission electron microscopy (TEM) and atomic force microscopy (AFM) were used to study the morphology and structure of the composite particles on drying. The AFM study confirms the non‐spherical shape of the particles. Thermogravimetric analysis shows improved thermal decomposition characteristics of the nanocomposite films. Copyright © 2015 John Wiley & Sons, Ltd.     

Symmetry systematics of pressure—induced phase transitions

Abstract

Most pressure induced phase transitions are diffusionless. Because of this, there exists a one-to-one correspondence between the positions of atoms in the parent and the product phases, which, therefore, show interesting symmetry relationships. In this paper, we have used these for discussing a symmetry classification of pressure induced phase transitions into four categories: iso-symmetric, group-subgroup, intersection group, and order-disorder transitions. Various examples illustrating this classification scheme are discussed. The importance of this classification is in understanding the mechanism of pressure indbced phase transitions, where both theoretical calculations and experimental measurements are employed to analyse related phenomena like softening of phonon modes, elastic instabilities, diffraction patterns, and orientation relations.     

Didecyldimethylammonium bromide (DDAB): a universal, robust, and highly potent phase-transfer catalyst for diverse organic transformations

Didecyldimethylammonium bromide (DDAB) has been scrutinized in comparison with traditional phase-transfer catalysts in variety of liquid-liquid reactions. It was found to be an exceptionally comprehensive, durable, and highly efficient phase-transfer catalyst (PTC) in a number of representative organic transformations such as C- and N-alkylations, isomerization, esterification, elimination, cyanation, bromination, and oxidation under very mild conditions of temperature and mixing. It was confirmed that DDAB is an exceedingly accessible and concurrently a highly liphophilic phase-transfer catalyst. This unprecedented characteristic renders DDAB to be a multipurpose catalyst that functions effectively both in mass transfer controlled and chemically controlled phase-transfer reactions.     

Insights into palladium-catalyzed cyanation of bromobenzene: additive effects on the rate-limiting step

Kinetic studies using reaction calorimetry were conducted under synthetically relevant conditions to study the effect of additives in the cyanation of bromobenzene catalyzed by palladium complexes. This work demonstrates that the addition of a catalytic amount of ZnBr(2) facilitates the reaction with an elimination of the induction period observed without additive. This study afforded a qualitative assessment of the effect of water on the rate-limiting step and the apparent reaction order in bromobenzene.     

Crystal and molecular structure of bis(o-phenylenethiourea)selenium(II)chloride dihydrate,C14H12N4S2Cl2Se·2H2O

The synthesis and crystal structure ofbis(o-phenylenethiourea)selenium(II)-chloride dihydrate, Se(C₇H₆N₂S)₂Cl₂·2H₂O are reported. The compound crystallizes in the monoclinic space group, P2₁/n, with four molecules per unit cell, the dimensions of which area=10.243(3),b=13.341(4),c=14.273(4) Å,=93.00(3)°,U=1947.76 ų. The structure was solved by direct methods and refined by full-matrix least-squares toR=0.039 andR _w =0.040 for 3314 unique reflections. Selenium displays two strong coordinations arising from the two sulfurs, Se-S(1)=2.191(1), Se-S(2)=2.206(1) Å, and S(1)-Se-S(2)=101.0(1)°, and four secondary interactions involving three chlorines and one sulfur. The complex occurs as a dimer with two sets of very weakly interacting bridging pairs S(2), S(2)^a; and Cl(2), Cl(2)^a, where a denotes the inversion related atom. Lattice stabilization is ensured by the extensive network of hydrogen bonds involving chlorines, water oxygens, and nitrogens of phenylenethiourea ligands.