共查询到20条相似文献,搜索用时 15 毫秒
1.
Babu S Rottereau M Nicolai T Gimel JC Durand D 《The European physical journal. E, Soft matter》2006,19(2):203-211
Off-lattice dynamic Monte-Carlo simulations were done of reversible cluster-cluster aggregation for spheres that form rigid
bonds at contact. The equilibrium properties were found to be determined by the life time of encounters between two particles
(te). te is a function not only of the probability to form or break a bond, but also of the elementary step size of the Brownian motion
of the particles. In the flocculation regime the fractal dimension of the clusters is df=2.0 and the size distribution has a power law decay with exponent τ=1.5. At larger values of te transient gels are formed. Close to the
percolation threshold the clusters have a fractal dimension df=2.7 and the power law exponent of the size distribution is τ=2.1. The transition between flocculation and percolation
occurs at a characteristic weight average aggregation number that decreases with increasing volume fraction. 相似文献
2.
Diffusion-limited cluster aggregation and gelation of hard spheres is simulated using off-lattice Monte Carlo simulations.
A comparison is made of the wall-particle correlation function with the particle-particle correlation function over a range
of volume fractions, both for the initial system of randomly distributed spheres and for the final gel state. For randomly
distributed spheres the correlation functions are compared with theoretical results using the Ornstein-Zernike equation and
the Percus-Yevick closure. At high volume fractions (φ > 40%) gelation has little influence on the correlation function, but
for φ < 10% it is a universal function of the distance normalized by correlation length (ξ) of the bulk. The width of the
depletion layer is about 0.5ξ. The concentration increases as a power law from the wall up to r ≈ ξ, where it reaches a weak maximum before decreasing to the bulk value. 相似文献
3.
Rottereau M Gimel JC Nicolai T Durand D 《The European physical journal. E, Soft matter》2005,18(1):15-19
The influence of the Brownian step size in off-lattice Monte Carlo simulations of the aggregation and gelation of spheres
is studied. It is found that the kinetics are strongly influenced if the step size is larger than the mean smallest distance
between the sphere surfaces. The structure of the clusters and the gels is influenced, but only over length scales smaller
than the step size. Using large step sizes leads to a narrower size distribution of the clusters. Implications of the present
results are discussed for simulations reported in the literature in which the Brownian step size was chosen equal to the sphere
diameter. 相似文献
4.
J.-C. Castaing C. Allain P. Auroy L. Auvray 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(1):61-70
Suspensions of nanosized hairy grains have been prepared by grafting long polydimethylsiloxane chains (molecular weight ) onto silica particles (radius ), dispersed into a good solvent of PDMS. Depending on the particle volume fraction, different rheological behaviors are observed.
In the very dilute regime, the suspensions are perfectly stable and the particles behave almost as hard spheres: flow penetration
inside the corona is then very weak. When the particle volume fraction goes to the close packing volume fraction, the suspension
viscosity does not diverge as for hard spheres due to the increase of flow penetration inside the corona and to corona entanglements.
The particles have then the same behavior as polymer stars having an intermediate number of arms (). Finally, in the concentrated regime (), the suspensions form irreversible gels. We shown that this unexpected gelation phenomenon is related to the presence of
the silica cores: grafted PDMS chains can adsorb onto different particles and form irreversible bonds between the cores. The
viscosity and elastic modulus evolutions during gelation are well described by the scalar percolation model of sol-gel transition.
Received 23 March 1998 相似文献
5.
P. Poulin J. Bibette D.A. Weitz 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(2):277-281
Aggregation mechanisms of emulsions at high initial volume fractions () is studied using light scattering. We use emulsion droplets which can be made unstable towards aggregation by a temperature
quench. For deep quenches and , the aggregation mechanism is identified as diffusion-limited cluster aggregation (DLCA). An ordering of the clusters, which
is reflected by a peak in the scattering intensity, is shown to result from the intercluster separation, exhibiting different
scaling than that observed at lower volume fractions. This manifests an increasing similarity to spinodal decomposition observed
as is increased. For and shallow quenches, different mechanisms, closer to spinodal decomposition, are observed. These results allow the subtle
boundaries between DLCA and spinodal decomposition to be explored.
Received: 7 April 1998 / Revised: 19 August 1998 / Accepted: 21 August 1998 相似文献
6.
We study gelation in suspensions of model colloidal particles with short-ranged attractive and long-ranged repulsive interactions by means of three-dimensional fluorescence confocal microscopy. At low packing fractions, particles form stable equilibrium clusters. Upon increasing the packing fraction the clusters grow in size and become increasingly anisotropic until finally associating into a fully connected network at gelation. We find a surprising order in the gel structure. Analysis of spatial and orientational correlations reveals that the gel is composed of dense chains of particles constructed from face-sharing tetrahedral clusters. Our findings imply that dynamical arrest occurs via cluster growth and association. 相似文献
7.
We have experimentally studied the dissociation/coalescence of internal Plateau borders (PBs) in simple monolayer bubble clusters, as a result of changing the liquid fraction. At large liquid content, the clusters consist of n bubbles of the same size, symmetrically placed around an internal n-sided PB (n-PB). On decreasing the liquid fraction we observed symmetry-breaking transitions in the 4- and 5-bubble clusters (but not in the 3-bubble cluster), followed by dissociation of the PBs. We used the Surface Evolver to determine the various equilibrium configurations of the corresponding two-dimensional wet clusters and their surface energies. The sequence of 4-bubble cluster configurations observed on varying the liquid fraction correlates qualitatively with that predicted on the basis of Surface Evolver calculations. The same is not true of the 5-bubble cluster. 相似文献
8.
Sabín J Prieto G Ruso JM Sarmiento F 《The European physical journal. E, Soft matter》2007,24(2):201-210
We present a study of the fractal dimension of clusters of large unilamellar vesicles (LUVs) formed by egg yolk phosphatidylcholine
(EYPC), dimyristoylphosphocholine (DMPC) and dipalmitoylphosphocholine (DPPC) induced by Ca2+ . Fractal dimensions were calculated by application of two methods, measuring the angular dependency of the light scattered
by the clusters and following the evolution of the cluster size. In all cases, the fractal dimensions fell in the range from
2.1 to 1.8, corresponding to two regimes: diffusion-limited cluster aggregation (DLCA) and reaction-limited cluster aggregation
(RLCA). Whereas DMPC clusters showed a typical transition from the RLCA to the DLCA aggregation, EYPC exhibited an unusual
behaviour, since the aggregation was limited for a higher concentration than the critical aggregation concentration. The behaviour
of DPPC was intermediate, with a transition from the RLCA to the DLCA regimes with cluster sizes depending on Ca2+ concentration. Studies on the reversibility of the aggregates show that EYPC and DPPC clusters can be re-dispersed by dilution
with water. DMPC does not present reversibility. Reversibility is evidence of the existence of secondary minima in the DLVO
potential between two liposomes. To predict these secondary minima, a correction of the DLVO model was necessary taking into
account a repulsive force of hydration. 相似文献
9.
We study the structure and the dynamics in the formation of irreversible gels by means of molecular dynamics simulation of a model system where the gelation transition is due to the random percolation of permanent bonds between neighboring particles. We analyze the heterogeneities of the dynamics in terms of the fluctuations of the self-intermediate scattering functions: in the sol phase close to the percolation threshold, we find that this dynamic susceptibility increases with the time until it reaches a plateau. At the gelation threshold this plateau scales as a function of the wave vector k as k(eta-2), with eta being related to the decay of the percolation pair connectedness function. At the lowest wave vector, approaching the gelation threshold it diverges with the same exponent gamma as the mean cluster size. These findings suggest an alternative way of measuring critical exponents in a system undergoing chemical gelation. 相似文献
10.
11.
AlSunaidi A Lach-Hab M Gonzalez AE Blaisten-Barojas E 《Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics》2000,61(1):550-556
The structure and aggregation kinetics of three-dimensional clusters composed of two different monomeric species at three concentrations are thoroughly investigated by means of extensive, large-scale computer simulations. The aggregating monomers have all the same size and occupy the cells of a cubic lattice. Two bonding schemes are considered: (a) the binary diffusion-limited cluster-cluster aggregation (BDLCA) in which only the monomers of different species stick together, and (b) the invading binary diffusion-limited cluster-cluster aggregation (IBDLCA) in which additionally monomers of one of the two species are allowed to bond. In the two schemes, the mixed aggregates display self-similarity with a fractal dimension d(f) that depends on the relative molar fraction of the two species and on concentration. At a given concentration, when this molar fraction is small, d(f) approaches a value close to the reaction-limited cluster-cluster aggregation of one-component systems, and when the molar fraction is 0.5, d(f) becomes close to the value of the diffusion-limited cluster-cluster aggregation model. The crossover between these two regimes is due to a time-decreasing reaction probability between colliding particles, particularly at small molar fractions. Several dynamical quantities are studied as a function of time. The number of clusters and the weight-average cluster size display a power-law behavior only at small concentrations. The dynamical exponents are obtained for molar fractions above 0.3 but not at or below 0.2, indicating the presence of a critical transition between a gelling to a nongelling system. The cluster-size distribution function presents scaling for molar fractions larger than 0.2. 相似文献
12.
The influence of surface forces on shear-induced tracer diffusion in mono and bidisperse suspensions
The shear-induced self-diffusivity of tracer particles of radius a
t = λa in a suspension of particles having a radius, a , is calculated by Stokesian dynamics for different values of the size ratio, λ , both in 2 and 3 dimensions in the binary-collision
regime. The self-diffusion is found to decrease strongly when the size ratio becomes quite different from unity. On the other
hand, for the same average distance of contact between two spheres, the presence of a soft force always increases greatly
the diffusion compared to the effect of a hard shell which is used to model the roughness. This is particularly true for tracer
particles smaller than the bath particles, where the shear-induced diffusion can be increased by many order of magnitudes
in the presence of a soft force. For suspensions of monodisperse particles we show that, for low volume fraction, the diffusion
coefficient is much smaller than the one predicted by the binary collision model, due to the existence of a layered structure.
On the contrary at higher volume fraction, many-body collisions strongly enhance the diffusion and it appears that the value
of the diffusion is quite sensitive to the presence of clusters of particles which are themselves determined by the range
of interparticle forces. 相似文献
13.
Mode-coupling theory (MCT) predicts the arrest of colloids in terms of their volume fraction, and the range and depth of the interparticle attraction. We discuss how the effective values of these parameters evolve under cluster aggregation. We argue that weak gelation in colloids can be idealized as a two-stage ergodicity breaking: first at short scales (approximated by the bare MCT) and then at larger scales (governed by MCT applied to clusters). The competition between the arrest and phase separation is considered in relation to recent experiments. We predict a long-lived "semiergodic" phase of mobile clusters, showing logarithmic relaxation close to the gel line. 相似文献
14.
A. Moncho-Jordá G. Odriozola F. Martınez-López A. Schmitt R. Hidalgo-Álvarez 《The European physical journal. E, Soft matter》2001,5(4):471-480
A sticking probability model based on the average cluster lifetime is employed for deducing a kernel capable to describe the
kinetics of computer simulated irreversible aggregation processes in two dimensions. The deduced kernel describes not only
the time evolution of the cluster size distribution for diffusion limited aggregation (DLCA) and reaction limited aggregation
(RLCA) but also for the entire transition region between both regimes. The model predicts a crossover to diffusion limited
cluster aggregation for all sticking probabilities at long aggregation times. The time needed for reaching the DLCA limit
increases for decreasing sticking probability.
Received 16 April 2001 and Received in final form 24 May 2001 相似文献
15.
Evaluation of Influence of Multiple Scattering Effect in Light-Scattering-Based Applications
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The extinction cross sections of a system containing two particles are calculated by the T-matrix method, and the results are compared with those of two single particles with single-scattering approximation. The necessity of the correction of the refractive indices of water and polystyrene for different incident wavelengths is particularly addressed in the calculation. By this means, the volume fractions allowed for certain accuracy requirements of single-scattering approximation in the light scattering experiment can be evaluated. The volume fractions calculated with corrected refractive indices are compared with those obtained with fixed refractive indices which have been rather commonly used, showing that fixed refractive indices may cause significant error in evaluating multiple scattering effect. The results also give a simple criterion for selecting the incident wavelength and particle size to avoid the 'blind zone' in the turbidity measurement, where the turbidity change is insensitive to aggregation of two particles. 相似文献
16.
通过CS状态方程及熵极大原理在多元胶体系统研究了杂质对硬球系统团簇成核临界条件的影响. 极少量元素或杂质的小胶球对系统成核的临界条件的影响也是不可忽略的: 成核的临界体积分量显著地降低;此外,研究还发现杂质对成核的临界尺寸影响较少. 相似文献
17.
F.R. Molino J.-F. Berret G. Porte O. Diat P. Lindner 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(1):59-72
We study the behavior under flow of soft spherical micelles forming a fcc phase at high volume fraction. Due to the size (300 ?) of the elementary objects, the structure can be investigated through
X-rays and neutron scattering, at rest and under flow in a Couette cell. Using scattering in two perpendicular directions,
different mechanisms of flow are identified. At intermediate shear (around 100 s-1) the system exhibits the so called layer sliding mechanism where two dimensional hexagonal compact planes of spheres align
themselves with the Couette cell walls. At lower shear rate, the fcc structure is locally preserved, and the flow is mediated by defects between crystallites. At high shear rate, we observe
the melting of the structure and a liquid-like structure factor. Moreover, we were able to use the existence of the layer
sliding regime to generate a fcc monocrystal by annealing the satcking faults between the decorrelated planes created by the layer sliding.
Received: 7 July 1997 / Received in final form: 16 January 1998 / Accepted: 5 March 1998 相似文献
18.
Dense cluster formation during aggregation and gelation of attractive slippery nanoemulsion droplets
Using time-resolved small angle neutron scattering, we have measured the wave-number-dependent structure factor S(q) of monodisperse nanoemulsions that aggregate and gel after we suddenly turn on a strong, short-range, slippery attraction between the droplets. At high q, peaks in S(q) appear as dense clusters of droplets form, and S(q) increases strongly toward low q, as these dense clusters become locked into a rigid gel network, despite the fluidity of the films between the droplets. The long-time high-q structure of nanoemulsion gels formed by slippery diffusion-limited cluster aggregation is universal in shape and remarkably independent of the droplet volume fraction, phi. 相似文献
19.
A. N. Novruzov O. R. Rakhmanova O. A. Novruzova A. E. Galashev 《Russian Journal of Physical Chemistry B, Focus on Physics》2008,2(1):115-122
The interaction of water clusters with acetylene molecules at T = 230 K was studied by the molecular dynamics method. The structure of clusters was analyzed by constructing Voronoi polyhedra. Water clusters interacting with C2H2 molecules are characterized by a diversity of H-bond orientations, a more uniform distribution of H-bonds over the cluster volume, a larger number of bonds per atom, and smaller bond lengths. The spectrum of bond lengths broadens as the number of acetylene molecules interacting with the water cluster increases. C2H2 molecules have a pressing action on water clusters. 相似文献
20.
This study was conducted to evaluate the effects of extra virgin olive (EVO) oil incorporation on the physicochemical properties and microstructure of surimi gels subjected to ultrasound-assisted water-bath heating. As the oil content was increased from 0 to 5 g/100 g, the breaking force and gel strength of the surimi gels significantly decreased, while the whiteness level exhibited the opposite tendency irrespective of the heating method. Compared with the traditional water-bath heating method, the ultrasonic heating promoted the unfolding of the α-helix structure and intensified the formation of β-sheet content and non-covalent bonds (ionic bonds, hydrogen bonds, and disulfide bonds), especially disulfide bonds, which contributed to the further crosslinking of the proteins and to gelation, thereby improving the gels’ strength. In addition, smaller cavities and compact microstructures were observed in the low-oil (≤3 g/100 g) surimi gels under ultrasonic treatment, which effectively prevented water migration in the gel network and resulted in a high water holding capacity and uniform water distribution. However, the ultrasonic treatment barely remedied the poor microstructures of the high-oil (>3 g/100 g) surimi gels owing to oil coalescence, which weakened the protein–protein interaction. In conclusion, ultrasonic treatment combined with water-bath heating significantly improved the gelation properties of the low-oil surimi gels, although it did not remarkably improve those of the high-oil gels. The choice of a suitable oil concentration could be of great importance for the production and functioning of surimi products via ultrasound-assisted treatments. 相似文献