396 research outputs found
Four particle cluster approximation for the Maier-Saupe model of the isotropic-nematic phase transition
The cluster variation theory for the Maier-Saupe model of the isotropic-nematic phase transition is extended to the four-particle level. As in the case of the Heisenberg ferromagnet, the irregularities of the three-particle cluster approximation applied to cubic lattices, where there are no triangles of nearest neighbors, disappear. The extension from three- to four-particle clusters yields improved values of all quantities, characteristic for the phase transition
Gelation as arrested phase separation in short-ranged attractive colloid-polymer mixtures
We present further evidence that gelation is an arrested phase separation in
attractive colloid-polymer mixtures, based on a method combining confocal
microscopy experiments with numerical simulations recently established in {\bf
Nature 453, 499 (2008)}. Our results are independent of the form of the
interparticle attractive potential, and therefore should apply broadly to any
attractive particle system with short-ranged, isotropic attractions. We also
give additional characterization of the gel states in terms of their structure,
inhomogeneous character and local density.Comment: 6 figures, to be published in J. Phys. Condens. Matter, special issue
for EPS Liquids Conference 200
Depletion potentials in highly size-asymmetric binary hard-sphere mixtures: Comparison of accurate simulation results with theory
We report a detailed study, using state-of-the-art simulation and theoretical
methods, of the depletion potential between a pair of big hard spheres immersed
in a reservoir of much smaller hard spheres, the size disparity being measured
by the ratio of diameters q=\sigma_s/\sigma_b. Small particles are treated
grand canonically, their influence being parameterized in terms of their
packing fraction in the reservoir, \eta_s^r. Two specialized Monte Carlo
simulation schemes --the geometrical cluster algorithm, and staged particle
insertion-- are deployed to obtain accurate depletion potentials for a number
of combinations of q\leq 0.1 and \eta_s^r. After applying corrections for
simulation finite-size effects, the depletion potentials are compared with the
prediction of new density functional theory (DFT) calculations based on the
insertion trick using the Rosenfeld functional and several subsequent
modifications. While agreement between the DFT and simulation is generally
good, significant discrepancies are evident at the largest reservoir packing
fraction accessible to our simulation methods, namely \eta_s^r=0.35. These
discrepancies are, however, small compared to those between simulation and the
much poorer predictions of the Derjaguin approximation at this \eta_s^r. The
recently proposed morphometric approximation performs better than Derjaguin but
is somewhat poorer than DFT for the size ratios and small sphere packing
fractions that we consider. The effective potentials from simulation, DFT and
the morphometric approximation were used to compute the second virial
coefficient B_2 as a function of \eta_s^r. Comparison of the results enables an
assessment of the extent to which DFT can be expected to correctly predict the
propensity towards fluid fluid phase separation in additive binary hard sphere
mixtures with q\leq 0.1.Comment: 16 pages, 9 figures, revised treatment of morphometric approximation
and reordered some materia
Structure and thermodynamics of colloid-polymer mixtures: a macromolecular approach
The change of the structure of concentrated colloidal suspensions upon
addition of non-adsorbing polymer is studied within a two-component,
Ornstein-Zernicke based liquid state approach. The polymers' conformational
degrees of freedom are considered and excluded volume is enforced at the
segment level. The polymer correlation hole, depletion layer, and excess
chemical potentials are described in agreement with polymer physics theory in
contrast to models treating the macromolecules as effective spheres. Known
depletion attraction effects are recovered for low particle density, while at
higher densities novel many-body effects emerge which become dominant for large
polymers.Comment: 7 pages, 4 figures; to be published in Europhys. Let
On the calculation of the self-diffusion coefficient of interacting Brownian particles
We consider two ways to calculate the self-diffusion coefficient of interacting Brownian particles. The first approach is based on the calculation of the mean square displacement of a Brownian particle starting from the Smoluchowski equation. In the second approach the self-diffusion
coefficient is obtained as the product of the thermodynamic driving force and the mobility. The advantages and limitations of the two methods are discussed
On the isotropic‐liquid crystal phase separation in a solution of rodlike particles of different lengths
The Onsager theory for the isotropic-anisotropic phase separation in a solution of rodlike particles is extended to the case of mixtures of such particles with different lengths. The concentration, composition, order parameters and orientation dependent thermodynamic quantities of the coexisting phases are calculated for the case of a mixture of rods of two different lengths for different length ratios. It is found that there is a significantly higher mole fraction of the longer rods in the anisotropic phase than in the isotropic phase. The order parameter of the longer rods is higher than in the one component case, whereas the order parameter of the shorter rods first increases and then decreases as the mole fraction of the longer rods is increased. All these features are accentuated as the length ratio of the two kinds of rods increases
Scaling of dynamics with the range of interaction in short-range attractive colloids
We numerically study the dependence of the dynamics on the range of
interaction for the short-range square well potential. We find that,
for small , dynamics scale exactly in the same way as thermodynamics,
both for Newtonian and Brownian microscopic dynamics. For interaction ranges
from a few percent down to the Baxter limit, the relative location of the
attractive glass line and the liquid-gas line does not depend on . This
proves that in this class of potentials, disordered arrested states (gels) can
be generated only as a result of a kinetically arrested phase separation.Comment: 4 pages, 4 figure
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