排序方式: 共有56条查询结果,搜索用时 31 毫秒
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Wyss HM Innerlohinger J Meier LP Gauckler LJ Glatter O 《Journal of colloid and interface science》2004,271(2):388-399
The aggregation of concentrated aqueous silica suspensions is characterized by means of static light scattering. We use an in situ destabilization mechanism based on the enzyme-catalyzed hydrolysis of urea. This method enables us to continuously and homogeneously change the interparticle potential from repulsive to attractive without disturbing the aggregation process. Moreover, our electrostatically stabilized suspensions can be destabilized by two different methods. In the first method, the pH is shifted toward the isoelectric point of the particles ( Delta pH method), thereby leading to a decrease of their surface charge. In the second method, the ionic strength is continuously increased at constant pH ( Delta I method), leading to a compression of the electrical double layer around the charged particles. A laboratory-built flat-cell light-scattering instrument is used, which allows fast data acquisition and an adjustment of the sample cell thickness. To circumvent multiple scattering effects, we use a very small sample thickness ( approximately 13 microm). In addition, the refractive index difference between the aqueous phase and the particles is reduced by adding sucrose to the liquid phase of our suspensions. We are able to characterize the structural changes at the very early stages of the destabilization process, where no significant effects are yet detected in macroscopic rheological measurements. While during the Delta pH destabilization, the scattering curve shows significant changes only after some characteristic delay time, it changes continuously during the Delta I destabilization. The latter is attributed to the formation of a weak pre-gel structure in the suspensions, as a shallow secondary minimum appears in the interparticle potential. Data are evaluated by using a HMSA square-well structure factor model. Results are in good agreement with those predicted from DLVO theory. 相似文献
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Cubic Schrödinger equations with small initial data (or small nonlinearity) and their spectral semi-discretizations in space are analyzed. It is shown that along both the solution of the nonlinear Schrödinger equation as well as the solution of the semi-discretized equation the actions of the linear Schrödinger equation are approximately conserved over long times. This also allows us to show approximate conservation of energy and momentum along the solution of the semi-discretized equation over long times. These results are obtained by analyzing a modulated Fourier expansion in time. They are valid in arbitrary spatial dimension. 相似文献
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Ludwig Gauckler Ernst Hairer Christian Lubich 《Communications in Mathematical Physics》2013,321(3):803-815
We consider multiscale Hamiltonian systems in which harmonic oscillators with several high frequencies are coupled to a slow system. It is shown that the oscillatory energy is nearly preserved over long times ${\varepsilon^{-N}}$ for arbitrary N > 1, where ${\varepsilon^{-1}}$ is the size of the smallest high frequency. The result is uniform in the frequencies and does not require non-resonance conditions. 相似文献
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Ultrastable particle-stabilized foams 总被引:1,自引:0,他引:1
Gonzenbach UT Studart AR Tervoort E Gauckler LJ 《Angewandte Chemie (International ed. in English)》2006,45(21):3526-3530
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Ludwig Gauckler 《计算数学(英文版)》2020,38(5):705-714
Trigonometric integrators for oscillatory linear Hamiltonian differential equations are
considered. Under a condition of Hairer & Lubich on the filter functions in the method,
a modified energy is derived that is exactly preserved by trigonometric integrators. This
implies and extends a known result on all-time near-conservation of energy. The extension
can be applied to linear wave equations. 相似文献
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Systematic valence changes in Pr1−xSrxMn1−yInyO3−δ upon cation substitution with Sr2+ and In3+ have been found using Mn K-edge and Pr L-edge X-ray absorption, and Mn LII,III and Pr MIV,V electron energy-loss spectroscopy. The average valence of the praseodymium ions is close to +3.0 and virtually constant over the sample set when the samples also contained manganese ions. Pr0.5Sr0.5InO3−δ showed a distinct increase in the praseodymium valence state. In contrast, the average valence of the manganese ions changed from the trivalent state to intermediate values between +3.0 and +4.0 and approached the tetravalent state depending on the level of substitution. The knowledge of the valence is required to understand the conduction mechanisms in the material due to the small polaron hopping (electronic conductivity) and motion of oxygen ions along the vacancies (ionic conductivity). Addition of strontium and indium led to the formation of oxygen vacancies. A previously assumed intermediate valence of praseodymium as causal factor for the higher oxygen catalytic activity cannot be confirmed with room temperature measurements. 相似文献
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Studart AR Amstad E Gauckler LJ 《Langmuir : the ACS journal of surfaces and colloids》2007,23(3):1081-1090
The stabilization of nanoparticles in concentrated aqueous suspensions is required in many manufacturing technologies and industrial products. Nanoparticles are commonly stabilized through the adsorption of a dispersant layer around the particle surface. The formation of a dispersant layer (adlayer) of appropriate thickness is crucial for the stabilization of suspensions containing high nanoparticle concentrations. Thick adlayers result in an excessive excluded volume around the particles, whereas thin adlayers lead to particle agglomeration. Both effects reduce the maximum concentration of nanoparticles in the suspension. However, conventional dispersants do not allow for a systematic control of the adlayer thickness on the particle surface. In this study, we synthesized dispersants with a molecular architecture that enables better control over the particle adlayer thickness. By tailoring the chemistry and length of these novel dispersants, we were able to prepare fluid suspensions (viscosity < 1 Pa.s at 100 s-1) with more than 40 vol % of 65-nm alumina particles in water, as opposed to the 30 vol % achieved with a state-of-the-art dispersing agent. This remarkably high concentration facilitates the fabrication of a wide range of products and intermediates in materials technology, cosmetics, pharmacy, and in all other areas where concentrated nanoparticle suspensions are required. On the basis of the proposed molecular architecture, one can also envisage other similar molecules that could be successfully applied for the functionalization of surfaces for biosensing, chromatography, medical imaging, drug delivery, and aqueous lubrication, among others. 相似文献
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Anna Evans Anja Bieberle-Hütter Henning Galinski Jennifer L. M. Rupp Thomas Ryll Barbara Scherrer René Tölke Ludwig J. Gauckler 《Monatshefte für Chemie / Chemical Monthly》2009,140(9):975-983
Abstract Micro-solid oxide fuel cells (micro-SOFC) are predicted to be of high energy density and are potential power sources for portable
electronic devices. A micro-SOFC system consists of a fuel cell comprising a positive electrode-electrolyte-negative electrode
(i.e. PEN) element, a gas-processing unit, and a thermal system where processing is based on micro-electro-mechanical-systems
fabrication techniques. A possible system approach is presented. The critical properties of the thin film materials used in
the PEN membrane are discussed, and the unsolved subtasks related to micro-SOFC membrane development are pointed out. Such
a micro-SOFC system approach seems feasible and offers a promising alternative to state-of-the-art batteries in portable electronics.
Graphical abstract Graphical Abstract text
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