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Alexander Schoth Caroline Wagner Lena L. Hecht Svenja Winzen Rafael Muñoz-Espí Heike P. Schuchmann Katharina Landfester 《Colloid and polymer science》2014,292(10):2427-2437
Hydrophilic silica particles need to be hydrophobized to be encapsulated in a polymeric environment, which can be achieved by different methods. We report on the relationship between different hydrophobization techniques of silica and the final structure of poly(methyl methacrylate)/silica hybrid nanoparticles obtained by miniemulsion polymerization. Hydrophobization by cetyltrimethylammonium chloride (CTMA-Cl) uses the ionic interaction between the positively charged ammonium salt and the negatively charged silica surface, as shown by isothermal titration calorimetry. In this case, the interaction between polymer and silica surface needs to be enhanced, so 4-vinylpyridine (4-VP) was used as a co-monomer. Alternatively, the condensation reactions of 3-methacryloxypropyltrimethoxysilane (MPS) and octadecyltrimethoxysilane (ODTMS) were used to provide a covalent bond to the silica surface. The condensation reaction of the trimethoxysilane groups onto the silica surface was proven by Fourier transform infrared spectroscopy and thermogravimetric analysis. Hybrid nanoparticles were successfully formed with silica particles functionalized with the different functionalization agents. However, the structure of the resulting hybrid particles (i.e., the distribution of the silica particles within the polymer matrix) depends on the agent. The MPS-functionalized silica particles copolymerize with poly(methyl methacrylate), leading to a fixation of the silica particles inside the polymer and to a homogeneous distribution. The CTMA-Cl- and ODTMS-functionalized silica particles cannot copolymerize, but aggregate at the interface, leading to a Janus-like structure. 相似文献
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Mark G Tauber A Laupert R Schuchmann HP Schulz D Mues A von Sonntag C 《Ultrasonics sonochemistry》1998,5(2):41-52
Terephthalate and Fricke dosimetry have been carried out to determine the sonolytic energy yields of the OH free radical and of its recombination product H2O2 in aqueous solutions under various operating conditions (nature of operating gas, power, frequency, temperature). For example, in the sonolysis of Ar-saturated terephthalate solutions at room temperature, a frequency of 321 kHz, and a power of 170 W kg-1, the total yield [G(.OH) + 2 G(H2O2)], equals 16 x 10(-10) mol J-1. This represents the total of .OH that reach the liquid phase from gas phase of the cavitating bubble. The higher the solute concentration, the lower the H2O2 production as more of the OH free radicals are scavenged, in competition with their recombination. Fricke dosimetry, in the absence and presence of Cu2+ ions, shows that the yield of H atom reaching the liquid phase is much lower, with G(H.) of the order of 3 x 10(-10) mol J-1. These sonolytic yields are smaller in solutions that are at the point of gas saturation, and increase to an optimum as the initial sonication-induced degassing and effervescence subsides. The probing of the sonic field has shown that the rate of sonolytic free-radical formation may vary across the sonicated volume depending on frequency and power input. 相似文献
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Winkelmann M Javadi A Miller R Schuchmann HP 《Journal of colloid and interface science》2012,372(1):202-206
Pendant drop and buoyant bubble methods have been used to study the surface characteristics of alkyl amines at the water/air surface. The investigated alkyl amines, triethylamine and octylamine, showed unusual changes in the surface tension as a function of time: an initially steep drop and a subsequent steady increase in the surface tension until a value close to the one of the pure water/air system was observed. This phenomenon is explained by the evaporation of the alkyl amines, for which several sets of experiments have been conducted with the pendant drop and buoyant bubble methods. Using an appropriate experimental protocol, the equilibrium adsorption behaviour of the two amines can be quantitatively measured. 相似文献
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In most applications, nanoparticles are required to be in a well-dispersed state prior to commercialisation. Conventional technology for dispersing particles into liquids, however, usually is not sufficient, since the nanoparticles tend to form very strong agglomerates requiring extremely high specific energy inputs in order to overcome the adhesive forces. Besides conventional systems as stirred media mills, ultrasound is one means to de-agglomerate nanoparticles in aqueous dispersions. In spite of several publications on ultrasound emulsification there is insufficient knowledge on the de-agglomeration of nanoparticulate systems in dispersions and their main parameters of influence. Aqueous suspensions of SiO2-particles were stressed up to specific energies EV of 10(4) kJ/m3 using ultrasound. Ultrasonic de-agglomeration of nanoparticles in aqueous solution is considered to be mainly a result of cavitation. Both hydrostatic pressure of the medium and the acoustic amplitude of the sound wave affect the intensity of cavitation. Furthermore, the presence of gas in the dispersion medium influences cavitation intensity and thus the effectiveness of the de-agglomeration process. In this contribution both, the influence of these parameters on the result of dispersion and the relation to the specific energy input are taken into account. For this, ultrasound experiments were carried out at different hydrostatic pressure levels (up to 10 bars) and amplitude values (64-123 microm). Depending on the optimisation target (time, energy input,...) different parameters limit the dispersion efficiency and result. All experimental results can be explained with the specific energy input that is a function of the primary input parameters of the process. 相似文献
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Prof. Dr. Stephan Schulz Raphaela Schäper Daniel Krech Daniella Schuchmann Dieter Bläser Roland Boese 《无机化学与普通化学杂志》2011,637(1):83-86
Lewis acid‐base adducts of the general type R2Zn(4‐tBuPy)x (R = Me 1 , iPr 2 , tBu 3 , Cp* 4 ; x = 1, 2) were obtained in high yields from reactions of ZnR2 with the Lewis base 4‐tBu‐Pyridine. Compounds 1 – 4 were characterized by multinuclear NMR (1H, 13C) and IR spectroscopy and elemental analyses, 1 and 4 also by X‐ray diffraction at single crystals. 相似文献
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H. Zegota M. N. Schuchmann C. Von Sonntag 《Journal of Radioanalytical and Nuclear Chemistry》1986,101(2):199-207
In the investigation of peroxyl radicals the pulse radiolysis technique can be used with some advantage to determine the rate of their unimolecular or bimolecular decay. If the identities of the products of the peroxyl radical reactions are known, pulse radiolysis often provides evidence for mechanistic details. The absorptions of the peroxyl radicals are neither very specific nor strong and optical detection is usually of little help. However, there are many peroxyl radical reactions which result in the formation of HO
2
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/H+O
2
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(pKa(HO
2
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)=4.7) or other acids. Thus in neutral and alkaline solutions such species can be monitored even quantitatively by the pulse conductometric method. Furthermore, O
2
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can be detected by its rapid reaction with tetranitromethane which yields the strongly absorbing nitroform anion. Since O
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is only a short-lived intermediate in neutral solutions, it can be distinguished from permanent acids which are often formed in peroxyl radical reactions. In alkaline solutions, where O
2
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is more stable, superoxide dismutase might be used with advantage to reduce its lifetime and to determine the yield of permanent acids. Some details of the fate of the peroxyl radicals derived from acetate, the -hydroxyethyl-peroxyl radicals, and the cyclopentylperoxyl radicals will be reviewed. 相似文献