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Lisa Roeder Philipp Bender Andreas Tschöpe Rainer Birringer Annette M. Schmidt 《Journal of polymer science. Part A, Polymer chemistry》2012,50(24):1772-1781
The mechanical characterization of complex soft matter by quasi-static magnetometry using nanoscopic magnetic probes is demonstrated for model hydrogels doped with two types of elongated magnetic nanoparticles. Chemically crosslinked poly(acrylamide) (PAAm) hydrogels serve as the matrix in which nickel nanorods or weakly magnetized hematite (α-Fe2O3) ellipsoids are embedded as local probes. We investigated the swelling behavior of the ferrogels in order to verify that their equilibrium swelling degree in water is not influenced by the probes, shows a good correlation with the Frenkel–Flory–Rehner model. The proposed magnetomechanical method relies on a correlation between the shear modulus of the PAAm hydrogel matrix and the coercive fields of the corresponding isotropic ferrogels. By extending the Stoner–Wohlfarth model for single-domain blocked magnetic particles by a term for particle rotation in an elastic matrix, information on the shear modulus of the matrix can be obtained. Comparison of the results with the expected relation from rubber elasticity theory illustrates both the general potential as well as the limits of the approach. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012 相似文献
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A cheap synthesis of the so‐called ‘decalin‐1,8‐diones’ started with the conjugate (1,4‐) addition of cyclohex‐2‐en‐1‐one derivatives to the γ‐position of the dilithium derivative (buta‐1,3‐diene‐1,1‐bis(olate)) of crotonic acid. Hydrogenation of these ‘1,4‐γ’ adducts and final cyclization afforded the enol tautomers of decalin‐1,8‐diones. Nucleophilic substitutions at these 3‐oxoenols by NH3 or primary amines created only monoamino products (namely, 3‐oxoenamines) whose reactions with OPCl3 yielded dihydro(1,3,2)oxazaphosphinin‐2‐one derivatives. The two regioisomers of a trimethyl‐3‐oxoenamine served as models for the constitutional assignments of the two rapidly interconverting (hence, individually NMR‐invisible), tautomeric trimethyl‐3‐oxoenols. Such methyl substitutions served to break the ‘pretended’ symmetry of ‘decalin‐1,8‐dione’. Hydrazine and 3‐oxoenols furnished oxygen‐free indazole derivatives whose N?H bonds exchanged with t1/2=ca. 0.00035 s at ca. ?58(9) °C. 相似文献
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Dr. Kazuhiko Amakawa Dr. Lili Sun Dr. Chunsheng Guo Dr. Michael Hävecker Pierre Kube Prof. Dr. Israel E. Wachs Soe Lwin Prof. Dr. Anatoly I. Frenkel Dr. Anitha Patlolla Prof. Dr. Klaus Hermann Prof. Dr. Robert Schlögl Dr. Annette Trunschke 《Angewandte Chemie (International ed. in English)》2013,52(51):13553-13557
Highly dispersed molybdenum oxide supported on mesoporous silica SBA‐15 has been prepared by anion exchange resulting in a series of catalysts with changing Mo densities (0.2–2.5 Mo atoms nm?2). X‐ray absorption, UV/Vis, Raman, and IR spectroscopy indicate that doubly anchored tetrahedral dioxo MoO4 units are the major surface species at all loadings. Higher reducibility at loadings close to the monolayer measured by temperature‐programmed reduction and a steep increase in the catalytic activity observed in metathesis of propene and oxidative dehydrogenation of propane at 8 % of Mo loading are attributed to frustration of Mo oxide surface species and lateral interactions. Based on DFT calculations, NEXAFS spectra at the O‐K‐edge at high Mo loadings are explained by distorted MoO4 complexes. Limited availability of anchor silanol groups at high loadings forces the MoO4 groups to form more strained configurations. The occurrence of strain is linked to the increase in reactivity. 相似文献
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Dr. Benjamin Frank Dr. Thomas P. Cotter Dr. Manfred E. Schuster Prof. Dr. Robert Schlögl Dr. Annette Trunschke 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(50):16938-16945
The effect of the gas‐phase chemical potential on surface chemistry and reactivity of molybdenum carbide has been investigated in catalytic reactions of propane in oxidizing and reducing reactant mixtures by adding H2, O2, H2O, and CO2 to a C3H8/N2 feed. The balance between surface oxidation state, phase stability, carbon deposition, and the complex reaction network involving dehydrogenation reactions, hydrogenolysis, metathesis, water‐gas shift reaction, hydrogenation, and steam reforming is discussed. Raman spectroscopy and a surface‐sensitive study by means of in situ X‐ray photoelectron spectroscopy evidence that the dynamic formation of surface carbon species under a reducing atmosphere strongly shifts the product spectrum to the C3‐alkene at the expense of hydrogenolysis products. A similar response of selectivity, which is accompanied by a boost of activity, is observed by tuning the oxidation state of Mo in the presence of mild oxidants, such as H2O and CO2, in the feed as well as by V doping. The results obtained allow us to draw a picture of the active catalyst surface and to propose a structure–activity correlation as a map for catalyst optimization. 相似文献
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