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1.
2.
de Campo L Yaghmur A Garti N Leser ME Folmer B Glatter O 《Journal of colloid and interface science》2004,274(1):251-267
In this paper we present the structural characterization of a five-component food-grade microemulsion containing Tween 80, R(+)-limonene, ethanol, glycerol, and water. Our main approach to investigating the microstructure of dense microemulsions, and how it can be influenced by the various components, was to employ small-angle neutron scattering and the new evaluation technique for dense, interacting systems, the Generalized Indirect Fourier Transformation. We started our investigation with the impact of glycerol and ethanol on Tween 80 micelles in water. We found that glycerol increases the aggregation number and withdraws the hydrating agents from the headgroup region of the surfactant, resulting in a higher packing density of molecules in a micelle at slightly increasing size. The same trend holds when the micelles are oil swollen and/or ethanol is present. Ethanol, on the other hand, redistributes mainly between water and the interface-headgroup region of the surfactant. Part of it replaces surfactant molecules in the micelles, which increases the available interface and results in a higher number of micelles with shrinking size. The same trend holds when the micelles are oil swollen and/or glycerol is present in the aqueous phase. We also investigated samples along the dilution of a mixture of surfactant and oil phase (R(+)-limonene and ethanol), which can be diluted with aqueous phase (mixture of water and glycerol) without the occurrence of phase separation. In some samples of this dilution most probably bicontinuous structures are present. To elucidate this point, we also employed dynamic light scattering, viscosity, and conductivity measurements. 相似文献
3.
Planer-Friedrich B Matschullat J Merkel BJ Roewer G Volke P 《Analytical and bioanalytical chemistry》2002,374(7-8):1191-1198
The formation of volatile organic and inorganic metals and metalloids in aquatic environments is a known, but not very intensively investigated, process. Several techniques have been developed over the past 10 years to determine these trace components. These techniques are of limited use in wetland environments, where samples have to be taken from the soil-water interface, and require an immediate sample analysis due to thermodynamic instabilities of the volatile metal(loid)s. This paper presents an innovative sampling technique for total concentrations of volatile metal(loid)s in wetlands, based on an in situ gas-water separation via a porous PTFE membrane and stabilising the volatile metal(loid)s in a liquid sorbent (NaOCl solution). Samples may thus be collected even at remote sites, where longer storage times have to be accounted for. The sampling system was tested by means of a laboratory facility simulating the generation of arsine and dimethyl arsine under abiotic conditions as well as under field conditions. Results for sampling efficiency, reproducibility, and long-term storage are presented. Application of the sampling system in the field is shown. 相似文献
4.
Mathematical Programming - Given two matroids $$\mathcal {M}_{1} = (E, \mathcal {B}_{1})$$ and $$\mathcal {M}_{2} = (E, \mathcal {B}_{2})$$ on a common ground set E with base sets $$\mathcal... 相似文献
5.
A. Ríos A. Lynggaard-Jensen H. S. Jacobsen R. Whiteman H. Wacheux B. Karlberg A. B. Lindholm T. Stenstrøm H. Berridge A. Boenke 《Accreditation and quality assurance》1999,4(12):B512-B517
ETACS is the official acronym for the European project "European Testing and Assessment of Comparability of On-line Sensors/Analysers". This project has three main objectives to achieve the comparability of performance data for sensors and analysers in the environmental field. First, to develop a test protocol for validation and comparison of the performance of on-line sensors/analysers. The test protocol is intended to be generic, that is independent of the specific sensors/analysers and the specific parameters to be monitored. Second, the practical testing of this test protocol to assess its applicability and to develop the techniques used. Finally, to achieve widespread acceptance of the test protocol by producer/suppliers, users and relevant authorities to assist its early adoption as an agreed European standard. Laboratory tests for producing the test protocol have been carried out and completed to check the applicability of such a protocol. 相似文献
6.
Dihydrothiinone 9a undergoes photocycloaddition regioselectively to all three C?C bonds of penta‐1,2,4‐triene ( 10 ), the relative stabilities of the biradical intermediates determining the product distribution. In contrast, cyclohexenone 9b and dihydropyranone 9c afford more complex mixtures of bicyclo[4.2.0]octanones, which also turn out to be less stable on chromatographic workup, reflecting the higher strain due to the shorter bond lengths (C? O and C? C vs. C? S) in the six‐membered rings, respectively. 相似文献
7.
The well-known method for the determination of selenium(IV), which is based on the cathodic stripping voltammetry of copper(I)
selenide, has been adapted for application at the thin-film mercury electrode on glassy carbon (TFME). Insufficient reproducibility
and sensitivity have been overcome by using a 0.1 mol/L HClO4 electrolyte solution containing 0.02 mol/L thiocyanate ions. Thiocyanate ions have been found to increase the peak height
of the selenium response and shift it to more positive potentials. This behaviour is explained by an adsorption of SCN– at the interface glassy carbon/Cu2Se and its action as an electron transfer catalyst between glassy carbon and copper(I) selenide. A 3σ-detection limit of 75
ng/L Se(IV) has been achieved. The relative standard deviation is 5.2% at 5 μg/L selenium(IV). The influence of cadmium(II), arsenic(III),
zinc(II), iron(III) and lead(II) ions on the selenium response has been studied. In case of lead ions, a new signal occurred
at more negative potentials than the reduction of Cu2Se. This signal, which is probably due to the reduction of PbSe, can also be used for the determination of selenium(IV).
Received: 13 November 1996 / Revised: 19 December 1996 / Accepted: 24 December 1996 相似文献
8.
The optical spectrum of diatomic RuC has been recorded from 17 800 to 24 200 cm(-1). Three previously unidentified excited electronic states were analyzed and identified as having Omega' = 0, Omega' = 2, and Omega' = 3. The Omega' = 3 state was determined to be a 3Delta3 state that is suggested to arise from a mixture of the 10sigma(2)11sigma(2)5pi(3)2delta(3)12sigma(1)6pi(1) and 10sigma(2)11sigma(1)5pi(3)2delta(3)12sigma(2)6pi(1) electronic configurations. Three additional bands belonging to the previously observed [18.1] (1)Pi<--X (1)Sigma(+) system were analyzed to obtain B(e) (')=0.558 244(48) cm(-1), alpha(e) (')=0.004 655(27) cm(-1), omegae' = 887.201(37) cm(-1), and omega(e) 'xe' = 5.589(7) cm(-1) for the 102Ru 12C isotopomer (1sigma error limits). A Rydberg-Klein-Rees analysis was then performed using the determined spectroscopic constants of the [18.1] 1Pi state, and similar analyses were performed for the previously observed states. The resulting potential energy curves are provided for the 100Ru 12C, 101Ru 12C, 102Ru 12C, and 104Ru 12C isotopic species. 相似文献
9.
10.
Dr. Julian Brunner Britta Maier Rose Rosenberg Sebastian Sturm Prof. Dr. Helmut Cölfen Dr. Elena V. Sturm 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(66):15242-15248
Applications in the fields of materials science and nanotechnology increasingly demand monodisperse nanoparticles in size and shape. Up to now, no general purification procedure exists to thoroughly narrow the size and shape distributions of nanoparticles. Here, we show by analytical ultracentrifugation (AUC) as an absolute and quantitative high-resolution method that multiple recrystallizations of nanocrystals to mesocrystals is a very efficient tool to generate nanocrystals with an excellent and so-far unsurpassed size-distribution (PDIc=1.0001) and shape. Similar to the crystallization of molecular building blocks, nonclassical recrystallization removes “colloidal” impurities (i.e., nanoparticles, which are different in shape and size from the majority) by assembling them into a mesocrystal. In the case of nanocrystals, this assembly can be size- and shape-selective, since mesocrystals show both long-range packing ordering and preferable crystallographic orientation of nanocrystals. Besides the generation of highly monodisperse nanoparticles, these findings provide highly relevant insights into the crystallization of mesocrystals. 相似文献