排序方式: 共有20条查询结果,搜索用时 15 毫秒
1.
Hähner G Zwahlen M Caseri W 《Langmuir : the ACS journal of surfaces and colloids》2005,21(4):1424-1427
Self-assembled alkyl chain based monolayers on mica are important for industrial and technological processes since they can be employed for an organic modification of the inorganic substrate. The conformational structure and orientational order of the films determine the interaction of the modified substrate with the environment and the chemical character and stability of its surface. We have studied the conformational order in ion exchanged dialkylammonium monolayers adsorbed on mica depending on the length of the alkyl chains systematically with near-edge X-ray absorption fine structure spectroscopy (NEXAFS). In addition, films were characterized by water contact angle measurements. The experimentally determined average tilt angles of the chains are discussed in terms of the degree of order. It was found that the absolute number of gauche defects in the films increases with decreasing chain length. 相似文献
2.
Mononuclear coordination compounds of the type [Pd(NH2trz)4]2+ with the counterions chloride, nitrate, trifluoromethanesulfonate, and methanesulfonate were synthesized and their structures identified with single‐crystal X‐ray diffraction. In case of the synthesis with methanesulfonate as the counterion the dominant product was of the generic formula [Pd2(NH2trz)3](CH3SO3)4, and the complex [Pd(NH2trz)4](CH3SO3)2 only emerged as a byproduct. While the structure of the byproduct could be analyzed by single‐crystal X‐ray diffraction, suitable crystals of the main product [Pd2(NH2trz)3](CH3SO3)4 could not be obtained. However, stoichiometry implies a polynuclear nature with NH2trz present in the rare μ3‐η1:η1:η1 coordination type, i.e. with NH2trz molecules coordinating to three palladium atoms. Accordingly, identification of solids by single‐crystal analysis alone can be misleading in particular with NH2trz as a ligand due to its versatile coordination behavior. Finally, analysis by differential scanning calorimetry (DSC) revealed that the complexes were thermally stable (the onset of decomposition well above 100 °C), with [Pd2(NH2trz)3](CH3SO3)4 being the most stable compound (onset of decomposition at 204 °C). 相似文献
3.
The specific surface area of a muscovite sample increases drastically after exposure to a LiNO3 solution, e.g., from 3.4 m2/g, corresponding to platelets of ca. 200 silicate layers, to 295 m2/g (platelets of ca. 2–3 silicate layers) after treatment at 180°C under atmospheric pressure for 46 h. The efficiency of the cleavage process decreases with decreasing temperature (down to 50°C). The LiNO3/H2O weight ratio is also very important: at 130°C and a reaction time of 46 h, for instance, a value in the range of 1.7–1.8 leads to the highest specific surfaces. The cleaved products have the form of strong papers that disperse readily in water. During the cleaving procedure, not only the particle thickness, but also the diameter decreases. There is no evidence of damage or partial dissolution of the silicate structure after cleavage, by IR spectroscopy and yield. The use of LiCl also leads to an increase in specific surface area, but the effect is weaker than in the case of LiNO3. Treatment with some other alkaline and alkaline earth nitrates and chlorides did not increase the specific surface area of muscovite significantly. 相似文献
4.
Ultrahigh specific surface area muscovite with different ions at the surface (Li+, Na+, K+, Rb+, Cs+, Ca2+, Sr2+, Ba2+, Cu2+) was treated with aqueous solutions of low molecular weight crown ethers and polymers with crown ether substituents. The adsorption was assessed by UV analysis of the supernatant solution, and with TGA and IR spectroscopy of the mica solids. In contrast to other layered silicates, the low molecular weight crown ethers show no affinity to any of the muscovite surfaces. The polymers can adsorb, however, depending on the type of surface cation. The results indicate that at least some of the crown ether moieties are complexed to surface cations and that the diameter of the ions at the surface plays an important role in the adsorption process. 相似文献
5.
Nanocomposites of lead sulfide and several polymers, especially poly(ethyleneoxide), were prepared by coprecipitation of lead sulfide and polymer, followed by a drying and pressing procedure. Such nanocomposites consist of ca. 90% w/w (or ca. 50% v/v) lead sulfide, of particle dimensions of 2–40 nm. The refractive index of these materials is on the order of 3 and therefore, to the authors' best knowledge, is the highest reported for any polymer composite. 相似文献
6.
Oat straw cellulose pulp was cationized in an etherification reaction with chlorocholine chloride. The cationized cellulose
pulp was then mechanically disintegrated in two process steps to obtain trimethylammonium-modified nanofibrillated cellulose
(TMA-NFC). The materials thus obtained were analyzed by elemental analysis, X-ray photoelectron spectroscopy (XPS), X-ray
diffraction (XRD), scanning electron microscopy (SEM) and other techniques. A higher nitrogen content of TMA-NFC samples was
found by XPS analysis than by elemental analysis, which indicates that the modification occurred mainly on the surface of
cellulose fibrils. XPS also confirmed the existence of ammonium groups in the samples. SEM provided images of very fine network
structures of TMA-NFC, which affirmed the positive effect of ionic charge on mechanical disintegration process. According
to XRD and SEM results, no severe degradation of the cellulose occurred, even at high reaction temperatures. Because of the
different properties of the cationic NFC compared to negatively charged native cellulose fibers, TMA-NFC may find broad applications
in technical areas, for instance in combination with anionic species, such as fillers or dyes. Indeed, TMA-NFC seems to improve
the distribution of clay fillers in NFC matrix. 相似文献
7.
Orphanou M Leontidis E Kyprianidou-Leodidou T Caseri W Krumeich F Kyriacou KC 《Journal of colloid and interface science》2006,302(1):170-177
The crystallization of PbS in aqueous solutions containing the surfactant sodium dodecyl sulfate (SDS) and hydrophilic polymers resulted in a novel type of metastable nanotubes, the walls of which consist of layers of ordered PbS nanoparticles, apparently separated by layers of surfactant molecules. Information on the mechanism of formation of these structures was obtained by focusing on the roles of the polymer, and of the insoluble lead dodecyl sulfate (Pb(DS)2) present in the system. TEM investigations of the early stages of crystallization revealed the coexistence of PbS and Pb(DS)2 precipitates, the latter being surprisingly important for nanotube formation, and allowed to follow the evolution of layered structures from combination of the two types of crystals. Six different hydrophilic polymers have been used, which interact with SDS with varying strengths. Surprisingly, and in contrast to previous hypotheses, layered nanostructures were observed in all polymer solutions, regardless of the strength of polymer-surfactant interactions. This indicates that, although the presence of a polymer is necessary, polymer-SDS interactions are not a driving force for the formation of the layered structures and nanotubes. On the contrary, the interactions between the polymer chains and the growing particles appear to be of the utmost importance. Results presented here can be interpreted in terms of two alternative mechanisms for layered nanostructure and nanotube formation. 相似文献
8.
Marie‐Luise Lechner Markus Trummer Irene Bräunlich Paul Smith Walter Caseri Frank Uhlig 《应用有机金属化学》2011,25(10):769-776
The efficiency and applicability of three different methods to synthesize polystannanes with different side chains are described. By means of dehydrogenative coupling utilizing the transition metal catalyst RhCl(PPh3)3 (Wilkinson's catalyst), n‐Bu2SnH2 reached the highest molar masses. Dehydrogenetive coupling in the presence of tetramethylethylenediamine could be best employed for (4‐n‐BuPh)2SnH2. Wurtz coupling using sodium in liquid ammonia was best suited for Ph2SnCl2. Next to the above‐mentioned educts, n‐Bu(Ph)SnX2 (X = H or Cl (as appropriate for the particular route) was used for polymerization resulting in one of so far rare example of asymmetric polystannanes with high molecular masses. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
9.
Markus Trummer Fabien Choffat Mario Rämi Paul Smith Walter Caseri 《Phosphorus, sulfur, and silicon and the related elements》2013,188(6):1330-1332
Abstract Polystannanes were prepared from H2SnR2 with the catalyst [RhCl(PPh3)3], or by reaction of Cl2SnR2 with Na in liquid ammonia. The polymers showed a characteristic peak in 119Sn NMR and UV-vis spectra, and a yellow color. Using common techniques, the polymers could be processed into films and oriented, the latter leading to a dichroism. The polystannanes are sensitive to light, more pronounced for R = alkyl than for R = aryl. GRAPHICAL ABSTRACT 相似文献
10.
Synthesis and Characterization of Surface-modified Rutile Nanoparticles And Transparent Polymer Composites Thereof 总被引:9,自引:0,他引:9
Nussbaumer René J. Caseri Walter Tervoort Theo Smith Paul 《Journal of nanoparticle research》2002,4(4):319-323
Nanoparticles of rutile, a crystal modification of titanium dioxide, were synthesized in strongly acidic solutions by hydrolysis of titanium tetrachloride. The particles of average diameter 2nm were coated in situ with a layer of dodecylbenzenesulfonic acid (DBSA) and isolated as a powder. Remarkably, dispersions of this powder in toluene were essentially transparent at the visible wavelengths but absorbed UV radiation over a broad wavelength range. The DBSA-coated rutile was also embedded in poly(styrene) and a poly(carbonate), resulting in polymer nanocomposites acting as visually transparent UV filters. 相似文献