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61.
Wilking JN Chang CB Fryd MM Porcar L Mason TG 《Langmuir : the ACS journal of surfaces and colloids》2011,27(9):5204-5210
The structural evolution and rheology of dense nanoemulsion gels, which have been formed by creating strong attractions between slippery nanodroplets, are explored as a function of steady shear rate using rheological small-angle neutron scattering (rheo-SANS). For applied stresses above the yield stress of the gel, the network yields, fracturing into aggregates that break and reform as they tumble and interact in the shear flow. The average aggregate size decreases with increasing shear rate; meanwhile, droplet rearrangements within the clusters, allowed by the slippery nature of the attractive interaction, increase the local density within the aggregates. At the highest shear rates, all clusters disaggregate completely into individual droplets. 相似文献
62.
Guérandel C Vernex-Loset L Krier G De Lanève M Guillot X Pierre C Muller JF 《Talanta》2011,84(1):133-140
Enhancing the flowing properties of fresh concrete is a crucial step for cement based materials users. This is done by adding polymeric admixtures. Such additives have enabled to improve final mechanicals properties and the development of new materials like high performance or self compacting concrete. Like this, the superplasticizers are used in almost cement based materials, in particular for concrete structures that can have a potential interaction with drinking water. It is then essential to have suitable detection techniques to assess whether these organic compounds are dissolved in water after a leaching process or not. The main constituent of the last generation superplasticizer is a PolyCarboxylate-Ester copolymer (PCE), in addition this organic admixture contains polyethylene oxide (free PEO) which constitutes a synthesis residue. Numerous analytical methods are available to characterize superplasticizer content. Although these techniques work well, they do not bring suitable detection threshold to analyze superplasticizer traces in solution with high mineral content such as leachates of hardened cement based materials formulated with superplasticizers. Moreover those techniques do not enable to distinguish free PEO from PCE in the superplasticizer.Here we discuss two highly sensitive analytical methods based on mass spectrometry suitable to perform a rapid detection of superplasticizer compounds traces in CEM I cement paste leachates: MALDI-TOF mass spectrometry, is used to determine the free PEO content in the leachate. However, industrial copolymers (such as PCE) are characterized by high molecular weight and polymolecular index. These two parameters lead to limitation concerning analysis of copolymers by MALDI-TOFMS. In this study, we demonstrate how pyrolysis and a Thermally assisted Hydrolysis/Methylation coupled with a triple-quadrupole mass spectrometer, provides good results for the detection of PCE copolymer traces in CEM I cement paste leachates. 相似文献
63.
Ying-Fen RanCarmen Blum Shi-Xia Liu Lionel Sanguinet Eric LevillainSilvio Decurtins 《Tetrahedron》2011,67(9):1623-1627
Highly selective formation of 2+2 macrocycle 1 from 2,5-bis(3-formyl-2-hydroxyphenyl)-1,3,4-oxadiazole and a diamine-functionalized tetrathiafulvalene derivative is reported. Its electronic properties have been studied experimentally by the combination of electrochemistry and UV-vis-NIR spectroscopy. Particularly, its largely extended π-conjugation renders this novel macrocycle simultaneously a good multielectron donor and a strong chromophore, which is rationalized on the basis of density functional theory. 相似文献
64.
Gerber I Oubenali M Bacsa R Durand J Gonçalves A Pereira MF Jolibois F Perrin L Poteau R Serp P 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(41):11467-11477
The nitric acid oxidation of multiwalled carbon nanotubes leading to surface carboxylic groups has been investigated both experimentally and theoretically. The experimental results show that such a reaction involves the initial rapid formation of carbonyl groups, which are then transformed into phenol or carboxylic groups. At room temperature, this reaction takes place on the most reactive carbon atoms. At higher temperatures a different mechanism would operate, as evidenced by the difference in activation energies. Experimental data can be partially related to first-principles calculations, showing a multistep functionalization mechanism. The theoretical aspects of the present article have led us to propose the most efficient pathway leading to carboxylic acid functional groups on the surface. Starting from mono-vacancies, it ends up with the synergistic formation of dangling -COOH groups and the enlargement of the vacancies. 相似文献
65.
Giovanelli E Leroux S Moisan L Carreyre H Thuéry P Buisson DA Meddour A Coustard JM Thibaudeau S Rousseau B Nicolas M Hellier P Doris E 《Organic letters》2011,13(15):4116-4119
Detailed investigations on one of the key steps of the superacidic fluorination of Vinca alkaloids that is the origin of C20' activation are reported. While two different pathways can be envisioned for the emergence of the transient secondary carbocationic intermediate, isotopic labeling experiments unambiguously revealed the involvement of a 1,2-hydride shift mechanism. 相似文献
66.
Köhler J Hemberger P Fischer I Piani G Poisson L 《The journal of physical chemistry. A》2011,115(50):14249-14253
The ultrafast dynamics of isolated 9-fluorenone was studied by femtosecond time-resolved photoionization and photoelectron spectroscopy. The molecule was excited around 264-266 nm into the S(6) state. The experimental results indicate that the excitation is followed by a multistep deactivation. A time constant of 50 fs or less corresponds to a fast redistribution of energy within the initially excited manifold of states, i.e., a motion away from the Franck-Condon region. Internal conversion to the S(1) state then proceeds within 0.4 ps. The S(1) state is long-lived, and only a lower bound of 20 ps can be derived. In addition, we computed excited state energies and oscillator strengths by TD-DFT theory, supporting the interpretation of the experimental data. 相似文献
67.
Letp be a prime and denote byA the modp Steenrod algebra. We determine the indecomposableA-module summands ofH*((ℤ/p))
d
;F
p
which admit the structure of an unstableA-algebra. In fact, it turns out that this is equivalent to the problem of determining those indecomposableA-module summands which arise as the modp cohomology of a space (or even a classifying space of a finite group). We reduce this problem to one in modular representation
theory, namely for whichd andp is the projective cover of the trivial one dimensional GL(d,F
p
) representationF
p
a permutation module. Our solution of this latter problem makes use of the classification of subgroups of GL(d,F
p
) acting transitively on (F
p
)
d
\{0} and hence depends on the classification of finite simple groups (on Feit-Thompson's odd order theorem ifp=2). 相似文献
68.
Yvon Pointud Claude Bernard Sébastien Touzain Lionel Astier Béatrice Sabatier Jean Juillard 《Journal of solution chemistry》1997,26(5):479-495
The standard Gibbs functions, enthalpies, and entropies for the formation of the complexes of monensin acid with monovalent
metal cations in acetonitrile were obtained using various methods (conductometry, potentiometry, and calorimetry). Complexation
is appreciable (from 2.0 to 4.5 in terms of association constant logarithm) and controlled mainly by the enthalpic effect.
Comparison with formation of the corresponding neutral complexes permits a comparison to the process of monensin mediated
transport of cation in membranes. A two-step process involving first the formation of the acidic complex is suggested. 相似文献
69.
Summary. The paper is devoted to the construction of a higher order Roe-type numerical scheme for the solution of hyperbolic systems
with relaxation source terms. It is important for applications that the numerical scheme handles both stiff and non stiff
source terms with the same accuracy and computational cost and that the relaxation variables are computed accurately in the
stiff case. The method is based on the solution of a Riemann problem for a linear system with constant coefficients: a study
of the behavior of the solutions of both the nonlinear and linearized problems as the relaxation time tends to zero enables
to choose a convenient linearization such that the numerical scheme is consistent with both the hyperbolic system when the
source terms are absent and the correct relaxation system when the relaxation time tends to zero. The method is applied to
the study of the propagation of sound waves in a two-phase medium. The comparison between our numerical scheme, usual fractional
step methods, and numerical simulation of the relaxation system shows the necessity of using the solutions of a fully coupled
hyperbolic system with relaxation terms as the basis of a numerical scheme to obtain accurate solutions regardless of the
stiffness.
Received October 7, 1994 / Revised version received September 27, 1995 相似文献
70.
Monika Kuemmel Cédric Boissière Lionel Nicole Christel Laberty-Robert Clément Sanchez David Grosso 《Journal of Sol-Gel Science and Technology》2008,48(1-2):102-112
TiO2, Al2O3, and ZrO2 patterns composed of ordered nano motifs of various morphologies (i.e. perforations (craters), rings, canyons, wires, dots, or channels) with typical lateral dimensions of less than 40 nm and thickness below 15 nm are presented. Simple chemical solution deposition (CSD) of molecular inorganic precursors and commercial block copolymers was used to create patterns on several substrate surfaces (bare, hydrophobized or gold covered silicon wafers and ITO). Self-assembly during evaporation and subsequent stabilization at 500 °C leads to the various nanostructures. Compared to other techniques for surface nano patterning, the present method has the advantage of being cheap, reproducible and easy to scale up and does not require specialized equipment. The type, dimension, and organization of these motifs were assessed by AFM, FE-SEM, spectroscopic ellipsometry, and GI-SAXS and are shown to depend on the conditions of preparation. Usage as model surfaces for modelling of wetting properties and as nanoelectrode arrays were investigated. 相似文献