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11.
Computer simulations based on Discrete Element Method have been performed in order to investigate the influence of interparticle interactions on the kinetics of self-assembly and the mechanical strength of nanoparticle aggregates.Three different systems have been considered.In the first system the interaction between particles has been simulated using the JKR (Johnson,Kendall and Roberts) contact theory,while in the second and third systems the interaction between particles has been simulated using van der Waals and electrostatic forces respectively.In order to compare the mechanical behaviour of the three systems,the magnitude of the maximum attractive force between particles has been kept the same in all cases.However,the relationship between force and separation distance differs from case to case and thus,the range of the interparticle force.The results clearly indicate that as the range of the interparticle force increases,the self-assembly process is faster and the work required to produce the mechanical failure of the assemblies increases by more than one order of magnitude. 相似文献
12.
John B. Fenn 《Journal of the American Society for Mass Spectrometry》1993,4(7):524-535
The formation of ions from the charged droplets produced in the several spray ionization techniques is viewed as an activated rate process involving field-assisted desorption, in accord with the ideas first set forth by Iribame and Thomson. The novel features of the present treatment are particularly relevant to the unique ability of electrospray ionization to transform large molecules in solution to free ions in the gas phase, with extensive multiple charging. These new features stem mainly from the realization that the spacing of charges on a desorbed ion must relate to the spacing of charges on the surface of the droplet whence it came. The consequences of this “rule” can account for the existence of maxima and minima in the number of charges on the ions of a particular species as well as the nature of the distribution of ions among the intervening charge states. They also explain the dependence of charge state on the configuration in solution of the parent molecule of the desorbed ion. In addition, they provide insight into the sequence in time at which ions in the various charge states leave an evaporating droplet. 相似文献
13.
D.A. Mantell S.B. Ryali B.L. Halpern G.L. Haller J.B. Fenn 《Chemical physics letters》1981,81(2):185-187
An uncollimated molecular beam (free jet) of CO and O2 molecules incident on a polycrystalline Pt surface at 775 K in vacuo produces vibrationally hot CO2 molecules at a density sufficient for infrared emission spectrometry. Analysis of spectra at a resolution of 0.1 cm?1 clearly shows that nascent product molecules have much more internal excitation than would be the case for equilibrium at the surface temperature. 相似文献
14.
We obtained, for the first time, high-resolution rotational distribution of CO2 collisionally excited by N2. The rotational distribution is non-Boltzmann, and the initial results suggest that surprisingly large impact parameter collisions contribute substantially to the collisional excitation, even though small impact parameter collisions are more effective, as expected. 相似文献
15.
16.
Infrared laser spectroscopy and time-of-flight mass spectrometry have been used to measure the rotational and translational distributions of HF and NH3 subliming from a polycrystalline sample of NH4F. The results of this study are compared with thermal desorption and gas-surface scattering experiments. 相似文献
17.
Dongliang Zhan Joan Rose John B. Fenn 《Journal of the American Society for Mass Spectrometry》1998,9(12):1241-1247
Experiments are described in which bare (completely desolvated) ions are separated from their source gas and mixed with a bath gas of any desired temperature and precisely controlled composition. The resulting mixture of ions and bath gas is transported by free jet expansion into a vacuum system for mass analysis to reveal the extent to which the ions have formed adducts with other species in the bath gas. Because the ions are separated from their source gas or vapor before they are mixed with the bath gas, the compositions of the bath gas and source gas are completely independent. Thus, one can examine solvation or adduction by any desired species contained in the bath gas without any interference from other species that might be present in the source gas. Reported here are results obtained on the solvation of electrospray ions of a small peptide, leucine-enkephalin, by water and several alkanols. One provocative finding is that a substantial fraction of ions thought to be singly charged monomers turned out to be doubly charged dimers. 相似文献
18.
Andreas Koschella Dominik Fenn Nicolas Illy Thomas Heinze 《Macromolecular Symposia》2006,244(1):59-73
Summary: The paper reviews recent developments in synthesis and characterization of regioselectively functionalized cellulose derivatives. It demonstrates the importance of protecting groups like triphenylmethyl- and thexyldimethylsilyl (TDMS) ethers in cellulose chemistry. The protected cellulose derivatives can be used for the preparation of 2,3-O-functionalized polymers. Moreover, the TDMS group opens up the synthesis of 3-O-ethers of cellulose that possess interesting properties in terms of structure in solution, water-solubility, and thermoreversible gelation. 相似文献
19.
Atsushi Nakagawa Dominik Fenn Andreas Koschella Thomas Heinze Hiroshi Kamitakahara 《Journal of Polymer Science.Polymer Physics》2011,49(21):1539-1546
This article describes detailed structure‐property relationships of 5 regioselectively methylated celluloses and 10 diblock cellulose derivatives with regioselective functionalization patterns: methyl 2,3,6‐tri‐O‐ ( 1 , 236MC), methyl 2,3‐di‐O‐ ( 2 , 23MC), methyl 2,6‐di‐O‐ ( 3 , 26MC), methyl 3‐O‐ ( 4 , 3MC), methyl 6‐O‐methyl‐cellulosides ( 5 , 6MC), methyl β‐D‐glucopyranosyl‐(1→4)‐2,3,6‐tri‐O‐methyl‐ ( 6 , G‐236MC), methyl β‐D‐glucopyranosyl‐(1→4)‐2,3‐di‐O‐methyl‐ ( 7 , G‐23MC), methyl β‐D‐glucopyranosyl‐(1→4)‐2,6‐di‐O‐methyl‐ ( 8 , G‐26MC), methyl β‐D‐glucopyranosyl‐(1→4)‐3‐O‐methyl‐ ( 9 , G‐3MC), methyl β‐D‐glucopyranosyl‐(1→4)‐6‐O‐methyl‐ ( 10 , G‐6MC), methyl β‐D‐glucopyranosyl‐(1→4)‐β‐D‐glucopyranosyl‐(1→4)‐2,3,6‐tri‐O‐methyl‐ ( 11 , GG‐236MC), methyl β‐D‐glucopyranosyl‐(1→4)‐β‐D‐glucopyranosyl‐(1→4)‐2,3‐di‐O‐methyl‐ ( 12 , GG‐23MC), methyl β‐D‐glucopy‐ranosyl‐(1→4)‐β‐D‐glucopyranosyl‐(1→4)‐2,6‐di‐O‐methyl‐ ( 13 , GG‐26MC), methyl β‐D‐glucopyranosyl‐(1→4)‐β‐D‐glucopyranosyl‐(1→4)‐3‐O‐methyl‐ ( 14 , GG‐3MC), and methyl β‐D‐glucopyranosyl‐(1→4)‐β‐D‐glucopyranosyl‐(1→4)‐6‐O‐methyl‐cellulosides ( 15 , GG‐6MC). Surface tension, differential scanning calorimetry, fluorescence, and dynamic light scattering measurements of aqueous solutions of compounds 1 – 15 revealed that there was no relationship between aggregation behaviors and gel formation, gelation occurred only when the hydrophobic environments formed by hydrophobic interactions between the sequences of 2,3,6‐tri‐O‐methyl‐glucopyranosyl units upon heating. The diblock structure consisting of cellobiosyl block and approx. ten 2,3,6‐tri‐O‐methyl‐glucopyranosyl units was of crucial importance for thermoreversible gelation of methylcellulose. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1539–1546, 2011 相似文献
20.
Electrospray dispersion of solutions into a bath gas can produce solute ions with many charges per molecule. In contrast to such multiple charging, it can also result in ‘fractional charging’ by which cluster ions are formed with more than one solute molecule per charge. Examples of such fractional charging or clustering are presented and discussed. In the case of arginine solutions, which are reported in some detail, ion masses corresponding to clusters containing as many as 24 solute molecules and up to four charges were identified. The number and size of these cluster ions increased markedly with increase in the initial solute concentration. When co-solutes consisting of acids, salts or bases were present, at up to millimolar concentrations in the initial solution, clustering was often strongly suppressed, especially by strong acids and their salts. This clustering phenomenon not only provides insight into the chemistry of solute precipitation in solution, but also offers a means of producing new kinds of clusters for experimental studies. 相似文献