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 共查询到19条相似文献,搜索用时 125 毫秒
1.
剪应力下弱作用势胶体颗粒聚团的特点   总被引:8,自引:3,他引:5  
探讨了不同剪应力下,具有Lennard-Jones势的胶体颗粒聚团的结构特性,包括簇团的大小分布,径向分布函数,分形维数和原子配位数。研究表明,在弱作用力下,胶体簇团的分布随剪应力的增加而趋向小簇团一边;径向分布函数曲线随剪应力的增加而降低,胡在近程距离内降低得最多;分形维数随剪应力的增加表现为先增加后减小的趋势,其值随模拟条件的不同而在1.9-2.4之间变动。剪应力“场”对分形维数的大小没有太大  相似文献   

2.
ELECTRON-TRANSFERINPOLYNUCLEARCYANO-BRIDGEDCOMPLEXOFTHETYPE[Co(Ⅲ)L_3-μ-Nc-FeⅡ)(CN)_5]~-(L=en)ShuZhongZHAN;XiaoYuanCHEN;QingJin?..  相似文献   

3.
XPSSTUDYONMo-Cu-SCLUSTERSJianPingLANG(DepartmentofChemistry,SuzhouUniversity,Suzhou215006)YongSuJIN,QingBingHUANG(CenterofAna...  相似文献   

4.
SYNTHESISOFOLIGONUCLEOTIDEd-(CCGTACGG)viaHELPMETHOD¥GenBinSHI,KaiXianCHEN,ZuShengXU,ZaiWanYANGandRuYunJI(ShanghaiInstituteofM...  相似文献   

5.
A FACILE TOTAL SYNTHESIS OF (±)-SELINA-3, 11-DIEN-9-OLAFACILETOTALSYNTHESISOF(±)-SELINA-3,11-DIEN-9-OLLiJunLIU;ZhaoMingXIONG;...  相似文献   

6.
SYNTHESISOFα-(SUBSTITUTEDPHENOXYACETOXY)ALKYLPHOSPHONATESHongWuHE;JunWang;ZhaoJieLIU(InstituteofOrganicSynthesis,CentralChina...  相似文献   

7.
合成了配合物trans-PtHXL2(L=PBu3、PPr3、Pet3;X=Cl-、Br-、I-、SCN-、CN-),并进行了1HNMR研究。测得Pt-H键的1H在高场的化学位移δH=-8~-24ppm;1J(Pt-H)=800~1500Hz和2J(P-H)=13.0~17.0Hz。鉴定了配合物的顺反异构和键合异构。研究了阴离子配体(X)及中性配体(L)对Pt-H键的δH、1J(Pt-H)及2J(P-H)的影响,Pt-H键长与Pt-HδH的关系。Pt-H化学位移与Pt-H的伸展振动频率呈线性关系。  相似文献   

8.
STUDIESONHETEROMACROCYCLICPOLYETHER(XIV)THESYNTHESISOFSELENACROWNETHERWITHHYDROXYGROUPANDDISELENA-AZA-CROWNETHERHanShengXu;Ju...  相似文献   

9.
CRYSTALSTRUCTUREOFA2DSHEET-LIKEμ-CYANIDO-OXAMIDATOBRIDGEDFe(III)-Cu(II)HETERNUCLEARCOMPLEX¥NeiFangWu;ZhongNingCHEN;JunQIUandW...  相似文献   

10.
SYNTHESIS OF NEW AMMONIUM-METAL(DNID)_2 COMPLEXES WITH LONG ALKYL CHAINJinXingPAN;YunQiLIUandDaoBenZHU(InstituteofChemistry.A...  相似文献   

11.
Orthokinetic aggregation of colloids trapped at the air–liquid interface was studied by direct imaging in a couette cell. This method allowed us to follow the temporal evolution of both the cluster-mass distribution and the cluster structure at a shear rate where Brownian aggregation is suppressed. The interactions between the monodisperse latex particles floating at the air–liquid interface were controlled either by varying the electrolyte concentration or by creating a bidisperse system through the addition of small particles. The results show that the clusters in all of the systems are characterized by a high fractal dimension, indicating that the clusters are rearranged and densified by the shear. Kinetic analysis suggests that aggregation of monodisperse systems mainly proceeds through homogeneous aggregation, i.e., large clusters sticking to other large clusters. The bidisperse system, finally, with a size ratio around 10, favored a more heterogeneous aggregation among small and large clusters throughout the aggregation process; a slightly lower fractal dimension was observed compared to the strongly aggregated monodisperse system.  相似文献   

12.
When a minimum on the potential energy surface is surrounded by multiple saddle points with similar energy barriers, the transition pathways with greater prefactors are more important than those that have similar energy barriers but smaller prefactors. In this paper, we present a theoretical formulation for the prefactors, computing the probabilities for transition paths from a minimum to its surrounding saddle points. We apply this formulation to a system of 2 degrees of freedom and a system of 14 degrees of freedom. The first is Brownian motion in a two-dimensional potential whose global anharmonicities play a dominant role in determining the transition rates. The second is a Lennard-Jones (LJ) cluster of seven particles in two dimensions. Low lying transition states of the LJ cluster, which can be reached directly from a minimum without passing through another minimum, are identified without any presumption of their characteristics nor of the product states they lead to. The probabilities are computed for paths going from an equilibrium ensemble of states near a given minimum to the surrounding transition states. These probabilities are directly related to the prefactors in the rate formula. This determination of the rate prefactors includes all anharmonicities, near or far from transition states, which are pertinent in the very sophisticated energy landscape of LJ clusters and in many other complex systems.  相似文献   

13.
This paper investigated average cluster sizes (ACS) and cluster size distributions (CSD) at different shear rates by Brownian dynamics in non-, bi-, and uni-polar systems with partly charged superfine particles, The investigation indicates that clusters in non- polar systems are the weakest and easiest to be damaged by increasing shear stresses; charged particles play important and different roles: in bi-polar system, it intends to strengthen clusters to some extent provided that the sign-like ions homogeneously arranged; in uni-polar system charged particles cracked the clusters into smaller ones, but the small clusters are strong to stand with larger shear stress. The relationship between ACS and shear rates follows power law with exponents in a range 0.18-0.28, these values are in a good agreement with experiment range but at the lower limit compared with other systems of non-metallic cluster particles.  相似文献   

14.
An unbiased algorithm for determining global minima of Lennard-Jones (LJ) clusters is proposed in the present study. In the algorithm, a global minimum is searched by using two operators: one modifies a cluster configuration by moving atoms to the most stable positions on the surface of a cluster and the other gives a perturbation on a cluster configuration by moving atoms near the center of mass of a cluster. The moved atoms are selected by employing contribution of the atoms to the potential energy of a cluster. It was possible to find new global minima for LJ506, LJ521, LJ536, LJ537, LJ538, and LJ541 together with putative global minima of LJ clusters of 10-561 atoms reported in the literature. This indicates that the present method is clever and efficient for cluster geometry optimization.  相似文献   

15.
We study the first breakage event of colloidal aggregates exposed to shear flow by detailed numerical analysis of the process. We have formulated a model, which uses stokesian dynamics to estimate the hydrodynamic interactions among the particles in a cluster, van der Waals interactions and Born repulsion to describe the normal interparticle interactions, and the tangential interactions through discrete element method to account for contact forces. Fractal clusters composed of monodisperse spherical particles were generated using different Monte Carlo methods, covering a wide range of cluster masses (N(sphere) = 30-215) and fractal dimensions (d(f) = 1.8-3.0). The breakup process of these clusters was quantified for various flow magnitudes (γ), under both simple shear and extensional flow conditions, in terms of breakage rate constant (K(B)), mass distribution of the produced fragments (FMD, f(m,k)), and critical stable aggregate mass (N(c)), defined as the largest cluster mass that does not break under defined flow conditions. The breakage rate K(B) showed a power law dependence on the product of the aggregate size and the applied stress, with values of the corresponding exponents depending only on the aggregate fractal dimension and the type of flow field, whereas the prefactor of the power law relation also depends on the size of the primary particles comprising a cluster. The FMD was fitted by Schultz-Zimm distribution, and the parameter values showed an analogous dependence on the product of the aggregate size and the applied stress similar to the rate constant. Finally, a power law relation between the applied stress and corresponding largest stable aggregate mass was found, with an exponent value depending on the aggregate fractal dimension. This unique and detailed analysis of the breakage process can be directly utilized to formulate a breakage kernel used in solving population balance equations.  相似文献   

16.
The interaction between particles in a system containing fractal clusters has been computationally simulated. The fractal structure of the system has been demonstrated to determine the kinetic characteristics of particle interaction. If a system in an N-dimensional space (N = 2, 3, 4) contains fractal clusters with the fractal dimension D > N-1, the rate of interaction of a free particle with particles belonging to clusters depends on their concentration according to the power law. The exponent gamma of this power law formally corresponds to the kinetic order of the reaction with respect to the concentration of particles belonging to the clusters. Its value is determined by the free surface of the clusters and depends on its fractal dimension D. The results of simulation qualitatively agree with the data on high, non-integral orders of many liquid phase molecular reactions characterized by self-organization of the medium via weak intermolecular interactions, such as hydrogen bonds.  相似文献   

17.
Solid-stabilized emulsions have been used as a model system to investigate the dynamics of charged microparticles with diameters of 1.1 microm at oil-water interfaces. Using confocal microscopy, we investigated the influences of interfacial curvature, cluster size, and temperature on the diffusion of solid particles. Our work suggests that a highly curved emulsion interface slows the motion of solid particles. This qualitatively supports the theoretical work by Danov et al. (Danov, K. D.; Dimova, R.; Pouligny, B. Phys. Fluids 2000, 12, 2711); however, the interfacial curvature effect decreases with increasing oil-phase viscosity. The diffusion of multiparticle clusters at oil-water interfaces is a strong function of cluster size and oil-phase viscosity and can be quantitatively related to fractal dimension. Finally, we report the influence of temperature and quantify the diffusion activation energy and friction factor of the particles at the investigated oil-water interfaces.  相似文献   

18.
A theory is developed which describes the optical properties of fractal clusters (i.e. of aggregates of non-trivial Hausdorff dimension consisting of interacting monomer particles). It is shown that with respect to these properties fractal clusters differ significantly from both gases and condensed media. The interaction between the monomers is assumed to be dipole-dipole. The theory is based on the self-consistent field equations; it takes into account the fluctuation nature of the fractal cluster (considerable probability for approach of monomers to each other despite an asymptotically zero integral density). An expression is obtained for the linear susceptibility. Combination of the monomers with the formation of a cluster entails the splitting, shift and broadening of the monomer spectra. These changes depend strongly on the fractal (Hausdorff) dimension of the cluster but do not depend on the number of monomers in it (for a cluster of non-trivial dimension). On the other hand, the monomers partially retain their individuality and the susceptibility — its quasi-resonance nature. Broadening, like the imaginary part of the susceptibility, does not depend on dissipation in an individual monomer. It is predicted that giant Raman scattering may occur at an impurity particle fixed near one of the cluster monomers when excitation takes place in the absorption band of the cluster. The enhancement factor for the scattering is also determined by the fractal dimension.  相似文献   

19.
Abstract

A review is given of the nature and implications of cluster formation in colloidal and molecular systems. We consider large clusters that can be described in terms of the fractal dimension and percolation exponents. The role of computer molecular simulation is discussed as a new method for probing random clustering of particles, short range structural correlations being of diminished importance here.  相似文献   

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