Search results for "surfaces"
showing 10 items of 2837 documents
Ethylene and phenylene bridged polysilsesquioxanes functionalized by amine and thiol groups as adsorbents of volatile organic compounds
2007
Abstract Ethylene and phenylene bridged polysilsesquioxane xerogels having amine and thiol groups attached to the surface have been obtained by the sol–gel method from 1,2-bis(triethoxysilyl)ethane or 1,4-bis(triethoxysilyl)benzene and functionalized silanes in the presence of an ammonium fluoride catalyst in an ethanol solution. The synthesized samples have a porous structure (700–850 m2/g) and a high content of functional groups (1.4–1.9 mmol/g). The obtained porous bridged polysilsesquioxanes exhibit a considerable affinity for adsorbing several organic compounds (n-hexane, n-heptane, benzene, cyclohexane, acetonitrile and triethylamine) from the gas phase. The sample with an ethylene br…
Homopolymerization of styrenic monomers and their copolymerization with ethylene using group 4 non‐metallocene catalysts
2020
Homopolymerization of styrenic monomers (St, p ‐Me‐St, p ‐t Bu‐St, p ‐t BuO‐St) and their copolymerization with ethylene, with the use of [( t Bu2O2NN′)ZrCl]2(μ‐O) (1 ) and ( t Bu2O2NN′)TiCl2 (2 ), where t Bu2O2NN′ = Me2N(CH2)2N(CH2‐2‐O−‐3,5‐t Bu2‐C6H2)2, is explored in the presence of MMAO and (i Bu)3Al/Ph3CB(C6F5)4. The ethylene/styrenic monomers copolymerization with 1 /MMAO produces exclusively copolymers with high activity and good comonomer incorporation whereas the other catalytic systems yield mixtures of copolymers and homopolymers. The use of p ‐alkyl styrene derivatives instead of styrene raises the catalytic activity, comonomer incorporation and molecular weights of the copolyme…
DFT study on complete ethylene decomposition on flat and stepped Pd
2010
Abstract We applied density functional theory (DFT) calculations to study ethylidyne (CCH 3 ) adsorption and decomposition to C and H over flat and stepped Pd surfaces. Our calculations show that ethylidyne is the most stable molecule among all the possible dehydrogenation or decomposition residues of ethylene. We discuss various possible reaction pathways for ethylidyne decomposition and point out that the most probable one is via ethynyl (CCH) species suggested also by experimental observations. Our calculations indicate that the presence of steps modify the potential energy surface by increasing the binding of most of the species, and also lowering the activation barrier for several reac…
Inner-shell excitation spectroscopy of closo-carboranes
1997
Oscillator strength spectra in the region of B 1s and C 1s excitation of three isomeric carborane cage compounds [closo-1,2-orthocarborane, closo-1,7-metacarborane, closo-1,12-paracarborane (C2B10H...
Colloidal Nanoplatelet/Conducting Polymer Hybrids: Excitonic And Material Properties
2016
WOS:000370678700053 Here we present the first account of conductive polymer/colloidal nanoplatelet hybrids. For this, we developed DEH-PPV-based polymers with two different anchor groups (sulfide and amine) acting as surfactants for CdSe nanoplatelets, which are atomically flat semiconductor nanocrystals. Hybridization of the polymers with the nanoplatelets in the solution phase was observed to cause strong photoluminescence quenching in both materials. Through steady-state photoluminescence and excitation spectrum measurements, photoluminescence quenching was shown to result from dominant exciton dissociation through charge transfer at the polymer/nanoplatelet interfaces that possess a sta…
Determination of Kinetic and Thermochemical Parameters of a Substitution Reaction at a Square-Planar Palladium(II) Complex in Water/AOT/n-Heptane Mic…
1995
Abstract The substitution reaction [Pd(bipy)(en)] 2+ + en → [Pd(en) 2 ] 2+ + bipy (where bipy = 2,2′-bipyridine and en = ethylenediamine) has been studied in water and water/AOT/ n -heptane microemulsions at various values of the molar ratio R ( R = [water]/[AOT]) by flow microcalorimetry. From calorimetric data, molar enthalpies of reaction and rate constants were obtained. These quantities indicate that, by increasing R , the reaction becomes less exothermic and its rate constant decreases, trending to the value observed in water. These features can be reasonably rationalized in terms of the peculiar solvation state of reactants inside the AOT reversed micelles and/or the peculiar physico…
Mechanisms of covalent dimerization on a bulk insulating surface
2017
Combining density functional theory and high resolution NC-AFM experiments, we have studied the on surface reaction mechanisms' responsible for the covalent dimerization of 4-iodobenzoic acid (IBA) organic molecules on the calcite (10.4), insulating surface. When annealed at 580 K, the Molecules assemble in one-dimensional chains of covalently bound dimers: The chains have a unique orientation and result from a complex set of processes, including a nominally rather. costly double dehalogenation reaction followed by dimerization. First, focusing on the latter two processes and using the nudged elastic band method, we analyze a number of possible mechanisms involving one and two molecules, an…
An experimental study of dynamic behaviour of graphite polycarbonatediol polyurethane composites for protective coatings
2013
Segmented polycarbonatediol polyurethane (PUPH) has been synthesized and modified with different amounts of graphite conductive filler (from 0 to 50 wt%). Thermal and dynamical thermal analysis of the composites clearly indicates changes in the polyurethane relaxations upon addition of graphite. Broadband dielectric spectroscopy has been used to study the dielectric properties of the (PUPH) and one composite in the frequency range from 10−2 to 107 Hz and in the temperature window of −140 to 170 ◦C. Relaxation processes associated with different molecular motions and conductivity phenomena (Maxwell–Wagner–Sillars and electrode polarization) are discussed and related to the graphite content
Determination of Geometry Arrangement of Copper Ions in HKUST-1 by XAFS During a Prolonged Exposure to Air
2017
We present an experimental investigation focused on the local structural changes taking place around Cu2+ions in metalâ organic framework (MOF) HKUST-1 for different times of exposure to air by XAFS (X-ray absorption fine structure). The analysis involves both XANES (X-ray absorption near edge structure) and EXAFS (extended X-ray absorption fine structure) regions around the Cu K-edge. Starting from the paddle-wheel structures proposed in literature, a more detailed description of the geometrical environment of Cu2+ions has been found. In particular, the paddle-wheel structure of a fresh sample, which means a pristine HKUST-1 material with a single water molecule weakly adsorbed on each C…
Processing and mechanical properties of organic filer-polypropylene composites
2005
The addition of organic fillers into thermoplastic polymers is an interesting issue, which has had growing consideration and experimentation during the last years. It can give rise to several advantages. First, the cost of these fillers is usually very low. Also, the organic fillers are biodegradable (thus contributing to an improved environmental impact), and finally, some mechanical and thermomechanical properties can be enhanced. In this study, the effect of the addition of different organic fillers on the mechanical properties and processability of an extrusion-grade polypropylene were investigated. The organic fillers came from natural sources (wood, kenaf, and sago) and were compared …