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261.
Pyrolysis models for burning solids in fire simulations are sensitive to the values of the activation energy, frequency factor, and reaction order that characterize the thermal decomposition of the solid to gaseous fuel, so direct measurement of these kinetic parameters is recommended, and simple methods are preferred. Three direct methods were evaluated with regard to the ability of their kinetic parameters to reproduce the thermal decomposition of five polymers measured by differential thermogravimetric analysis using the reaction order model. It was found that the two multiple heating rate methods produced identical, physically based kinetic parameters, while the peak property method produced non-physical kinetic parameters. However, all of these kinetic parameters in a single-step reaction order model gave reasonably good conversion histories for non-charring and moderately charring polymers. For a highly charring polymer, the conversion histories were poorly described without a multiple step reaction. The temperature at the maximum rate of conversion was found to be essentially independent of the reaction order, which decouples the frequency factor from the reaction order in the direct kinetic methods. Any of the direct methods are sufficiently accurate to obtain kinetic parameters for pyrolysis models because of the inherent spatial and temporal averaging of reaction rates at the burning surface of a thick solid and the uncertainty in the heat transfer mechanisms and thermo-physical parameters used in the models. 相似文献
262.
We describe the assembly of two-component, hydrogel microparticle (microgel) monolayer films onto solid substrates via passive Coulombic adsorption from solution. By using two different microgel types with nearly identical sizes but different degrees of softness, the influence of particle deformation on film composition was determined. Determination of the microgel properties using a variety of light scattering techniques allowed for predictions of the film composition as a function of solution composition using a random sequential adsorption (RSA) model. The films were then studied via atomic force microscopy (AFM), and surface coverage and population statistics were determined from the images and compared to the model predictions. Deviations from the predicted particle adsorption behavior can be directly traced to differences in particle softness, deformation, and particle footprint following adsorption, which biases the particle coverage to the more rigid (smaller footprint) particles. Furthermore, by using a mixture of degradable and nondegradable core/shell particles, the identity of the particles can be unambiguously determined by measuring AFM height changes following erosion of the core from the microgels. These results show that, regardless of the solution diffusion properties of soft particles, their competition for surface adsorption from a binary mixture is largely dictated by their interactions with the surface and their deformation at the surface. 相似文献
263.
Dr. Vu Thi Ngan Prof. Ewald Janssens Dr. Pieterjan Claes Prof. Jonathan T. Lyon Dr. André Fielicke Prof. Dr. Minh Tho Nguyen Prof. Dr. Peter Lievens 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(49):15788-15793
We report on the structural, electronic, and magnetic properties of manganese‐doped silicon clusters cations, SinMn+ with n=6–10, 12–14, and 16, using mass spectrometry and infrared spectroscopy in combination with density functional theory computations. This combined experimental and theoretical study allows several structures to be identified. All the exohedral SinMn+ (n=6–10) clusters are found to be substitutive derivatives of the bare Sin+1+ cations, while the endohedral SinMn+ (n=12–14 and 16) clusters adopt fullerene‐like structures. The hybrid B3P86 functional is shown to be appropriate in predicting the ground electronic states of the clusters and in reproducing their infrared spectra. The clusters turn out to have high magnetic moments localized on Mn. In particular the Mn atoms in the exohedral SinMn+ (n=6–10) clusters have local magnetic moments of 4 μB or 6 μB and can be considered as magnetic copies of the silicon atoms. Opposed to other 3d transition‐metal dopants, the local magnetic moment of the Mn atom is not completely quenched when encapsulated in a silicon cage. 相似文献
264.
265.
Thermoresponsive hydrogel nanoparticles composed of poly(N-isopropylmethacrylamide) (pNIPMAm) and the disulfide-based cross-linker N,N'-bis(acryloyl)cystamine (BAC) have been prepared using a redox-initiated, aqueous precipitation polymerization approach, leading to improved stability of the disulfide bond compared to traditional thermally-initiated methods. The resultant particles demonstrate complete erosion in response to reducing conditions or thiol competition. This stands in contrast to the behavior of thermally-initiated particles, which retain a cross-linked network following disulfide cleavage due to uncontrolled chain-branching and self-cross-linking side reactions. The synthetic strategy has also been combined with the non-degradable cross-linker N,N-methylenebisacrylamide (BIS) to generate "co-cross-linked" pNIPMAm-BAC-BIS microgels. These particles are redox-responsive, swell upon BAC cross-link scission and present reactive thiols. This pendant thiol functionality was demonstrated to be useful for conjugation of thiol-reactive probes and in reversible network formation by assembling particles cross-linked by disulfide linkages. 相似文献
266.
Laser-ablated titanium atoms react with CX4 (X = F and Cl) to produce triplet state XC/TiX3 complexes trapped in an argon matrix. Products are identified by their infrared spectra and comparison to theoretically predicted vibrations. Density functional theory calculations converge to C(3v) symmetry structures for these lowest-energy products. The two unpaired electrons in the carbon 2p orbitals are shared with empty titanium d orbitals leading to degenerate singly occupied pi molecular orbitals and an electron-deficient triple bond between the carbon and titanium centers, on the basis of DFT bonding analysis and spin density calculations. The carbon-titanium distances are near typical C=Ti double bond lengths, and the C-X bonds in the resulting products are shorter than in the CX4 precursors. It appears that X lone-pair conjugation contributes to the C-X bond strength and somewhat to the C-Ti bond, and Cl does better in this regard than F. 相似文献
267.
M. Mougenot P. Andreazza C. Andreazza-Vignolle R. Escalier Th. Sauvage O. Lyon P. Brault 《Journal of nanoparticle research》2012,14(2):672
Nanostructured platinum-carbon thin films were prepared by magnetron co-sputtering method for designing efficient catalytic
thin films, like fuel cells electrodes. The in-depth morphology of composite films was studied using surface sensitive X-ray
techniques (grazing incidence small-angle scattering and reflectivity), consolidated by electron microscopy investigations.
This study elucidates the growth mode of co-sputtered platinum-carbon thin film: 2-nm-sized platinum clusters are growing
in surrounding simultaneously growing carbon columns (20-nm diameter range). In particular, the platinum cluster growth and
distribution in the plane of the substrate surface are driven by surface diffusion and coalescence phenomena. Finally, this
anisotropic distribution of platinum clusters correlated to the textured morphology of carbon matrix leads to a catalytic
thin film morphology very suitable for electrochemical processes in fuel cell electrodes. 相似文献