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The benzene dimer is the simplest prototype of pi-pi interactions and has been used to understand the fundamental physics of these interactions as they are observed in more complex systems. In biological systems, however, aromatic rings are rarely found in isolated pairs; thus, it is important to understand whether aromatic pairs remain a good model of pi-pi interactions in clusters. In this study, ab initio methods are used to compute the binding energies of several benzene trimers and tetramers, most of them in 1D stacked configurations. The two-body terms change only slightly relative to the dimer, and except for the cyclic trimer, the three- and four-body terms are negligible. This indicates that aromatic clusters do not feature any large nonadditive effects in their binding energies, and polarization effects in benzene clusters do not greatly change the binding that would be anticipated from unperturbed benzene-benzene interactions, at least for the 1D stacked systems considered. Three-body effects are larger for the cyclic trimer, but for all systems considered, the computed binding energies are within 10% of what would be estimated from benzene dimer energies at the same geometries. 相似文献
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A generalized technique for the encapsulation of nano‐sized NiO particles by styrene‐2‐hydroxyethyl methacrylate copolymer 下载免费PDF全文
M. Shamim Hossan M. Abdur Rahman Klaus Tauer Hideto Minami Hasan Ahmad 《先进技术聚合物》2015,26(9):1047-1052
Encapsulation of nickel oxide (NiO) particles is of great interest to the researchers as such modification produces remarkable improvement in properties and versatility in application potential. In this investigation, nanosized NiO particles were first prepared by calcination of nickel hydroxide precursor obtained using a simple liquid‐phase process. The produced NiO particles were stabilized with oleic acid and then treated with tetraethylorthosilicate to produce NiO/SiO2 composite seed particles. Finally tri‐layered inorganic/organic composite particles were prepared by seeded copolymerization of styrene and 2‐hydroxyethyl methacrylate (HEMA) in the presence of NiO/SiO2 composite seed particles. The produced composite particles named as NiO/SiO2/P(S‐HEMA) were colloidally stable, and the obtained particles were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, X‐ray diffraction, X‐ray photoelectron spectroscopy and thermogravimetric analyses. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
3.
Johannes Tauer Heinrich Kofler Elisabeth Schwarz Ernst Wintner 《Central European Journal of Physics》2010,8(2):242-248
Laser ignition is considered to be one of the most promising future concepts for internal combustion engines. It combines the legally required reduction of pollutant emissions and higher engine efficiencies. The igniting plasma is generated by a focused pulsed laser beam. Having pulse durations of a few nanoseconds, the pulse energy E p for reliable ignition amounts to the order of 10 mJ. Different methods of laser ignition with an emphasis on fiber-based systems will be discussed and evaluated. 相似文献
4.
E Wenisch C Tauer A Jungbauer H Katinger M Faupel P G Righetti 《Journal of chromatography. A》1990,516(1):133-146
Isoforms of human monoclonal antibodies against the gp-41 of AIDS virus and of human recombinant superoxide dismutase have been purified to homogeneity by isoelectric focusing (IEF) in a multi-compartment electrolyser with isoelectric, immobiline membranes. This system allows the processing of large sample volumes and gram-scale protein loads and can resolve isoforms as close as 0.001 in pI difference. The purification progress was usually monitored by analytical IEF in immobilized pH gradients (IPG). Capillary zone electrophoresis (CZE) was applied to the monitoring of the content of each chamber of the electrolyser. CZE was found to be superior in terms of speed of analysis and quantification (but only by UV reading at 200-210 nm, i.e., in the region of the peptide bond) but, notwithstanding the millions of theoretical plates reported, was no match for the resolving power of IPGs, at least for protein analysis. When compared also with chromatofocusing, the resolving power decreases in the order IPG greater than CZE much greater than chromatofocusing. 相似文献
5.
A new class of colloidal polymeric particles consisting of polystyrene spheres grown in a poly(N‐isopropyl acrylamide) precursor scaffold is synthesized via redox‐initiated heterophase polymerization. The morphology and thermoresponsiveness of these assemblies is proven by electron microscopy investigations and temperature‐dependent measurements of the change of both the speed of sound travelling through the dispersion and the hydrodynamic particle size. Electron microscopy (EM) micrographs (transmission and scanning EM as well cryo‐scanning EM) prove the existence of colloidal clusters when the freeze‐dried copolymer is redispersed in pure water. The clusters have a size of several micrometers, contain about 800 polystyrene particles with diameter below 100 nm, and show a highly reproducible thermoresponsive behavior with a lower critical solution temperature corresponding to that of pure poly(N‐isopropyl acrylamide).
6.
Klaus Tauer Hugo Hernandez Steffen Kozempel Olga Lazareva Pantea Nazaran 《Colloid and polymer science》2008,286(5):499-515
The application of atypical experimental methods such as conductivity measurements, optical microscopy, and nonstirred polymerizations
to investigations of the ‘classical’ batch ab initio emulsion polymerization of styrene revealed astonishing facts. The most
important result is the discovery of spontaneous emulsification leading to monomer droplets even in the quiescent styrene
in water system. These monomer droplets with a size between a few and some hundreds of nanometers, which are formed by spontaneous
emulsification as soon as styrene and water are brought into contact, have a strong influence on the particle nucleation,
the particle morphology, and the swelling of the particles. Experimental results confirm that micelles of low-molecular-weight
surfactants are not a major locus of particle nucleation. Brownian dynamics simulations show that the capture of matter by
the particles strongly depends on the polymer volume fraction and the size of the captured species (primary free radicals,
oligomers, single monomer molecules, or clusters). 相似文献
7.
A light microscopy study confirms spontaneous emulsification at the quiescent, thermally equilibrated interface between pure oil and pure water during the chemical equilibration period. The process is qualitatively explained within the frame of the classical nucleation theory assuming a mixed interface layer between the two liquids in contact allowing supersaturation. 相似文献
8.
Heterophase polymerization in combination with ceric ion redox initiation offers some unique features with respect to the preparation of block copolymers and block copolymer particles. Various kinds of amphiphilic multi-block copolymers as well as electrosterically or sterically stabilized particles are easy accessible. A special feature of these particles is that they may consists of two different hydrophilic blocks and thus, leading to particles with a structured hydrophilic shell. The amphiphilic multiblock copolymers are used to form a new class of polymer dispersions by self-organization so-called polymeric colloidal complexes. In general, the particles of these complexes are structured and exhibit very often multiple morphologies. This principle of formation of polymer colloids is an easy way to prepare particles with an unusual morphology such as Janus-type particles. 相似文献
9.
Mass transfer across interfaces greatly determines the kinetics of heterophase polymerization. All molecules in the system can cross any interface as long as they possess enough energy to overcome barriers such as interfacial tension, chemical potentials, etc. Two main groups of mathematical approaches have been used to model mass transfer: macroscopic deterministic and molecular stochastic. Macroscopic modeling may use fundamental laws, thermodynamic expressions and empirical or semi‐empirical equations. Molecular models are based on the discrete character of nature and include stochastic simulation, BD or MD. Special emphasis is placed on the most relevant molecular transfer processes observed in free‐radical emulsion polymerization.
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