109 research outputs found
Short-time diffusion in concentrated bidisperse hard-sphere suspensions
Diffusion in bidisperse Brownian hard-sphere suspensions is studied by
Stokesian Dynamics (SD) computer simulations and a semi-analytical theoretical
scheme for colloidal short-time dynamics, based on Beenakker and Mazur's method
[Physica 120A, 388 (1983) & 126A, 349 (1984)]. Two species of hard spheres are
suspended in an overdamped viscous solvent that mediates the salient
hydrodynamic interactions among all particles. In a comprehensive parameter
scan that covers various packing fractions and suspension compositions, we
employ numerically accurate SD simulations to compute the initial diffusive
relaxation of density modulations at the Brownian time scale, quantified by the
partial hydrodynamic functions. A revised version of Beenakker and Mazur's
-scheme for monodisperse suspensions is found to exhibit
surprisingly good accuracy, when simple rescaling laws are invoked in its
application to mixtures. The so-modified scheme predicts
hydrodynamic functions in very good agreement with our SD simulation results,
for all densities from the very dilute limit up to packing fractions as high as
.Comment: 12 pages, 6 figure
Rotational self-diffusion in suspensions of charged particles: Revised Beenakker-Mazur and Pairwise Additivity methods versus numerical simulations
To the present day, the Beenakker-Mazur (BM) method is the most comprehensive
statistical physics approach to the calculation of short-time transport
properties of colloidal suspensions. A revised version of the BM method with an
improved treatment of hydrodynamic interactions is presented and evaluated
regarding the rotational short-time self-diffusion coefficient, , of
suspensions of charged particles interacting by a hard-sphere plus screened
Coulomb (Yukawa) pair potential. To assess the accuracy of the method,
elaborate simulations of have been performed, covering a broad range of
interaction parameters and particle concentrations. The revised BM method is
compared in addition with results by a simplifying pairwise additivity (PA)
method in which the hydrodynamic interactions are treated on a two-body level.
The static pair correlation functions re- quired as input to both theoretical
methods are calculated using the Rogers-Young integral equation scheme. While
the revised BM method reproduces the general trends of the simulation results,
it systematically and significantly underestimates the rotational diffusion
coefficient. The PA method agrees well with the simulation data at lower volume
fractions, but at higher concentrations is likewise underestimated. For a
fixed value of the pair potential at mean particle distance comparable to the
thermal energy, increases strongly with increasing Yukawa potential
screening parameter.Comment: 24 pages, 13 figure
Glass transition of charged particles in two-dimensional confinement
The glass transition of mesoscopic charged particles in two-dimensional
confinement is studied by mode-coupling theory. We consider two types of
effective interactions between the particles, corresponding to two different
models for the distribution of surrounding ions that are integrated out in
coarse-grained descriptions. In the first model, a planar monolayer of charged
particles is immersed in an unbounded isotropic bath of ions, giving rise to an
isotropically screened Debye-H\"uckel- (Yukawa-) type effective interaction.
The second, experimentally more relevant system is a monolayer of negatively
charged particles that levitate atop a flat horizontal electrode, as frequently
encountered in laboratory experiments with complex (dusty) plasmas. A steady
plasma current towards the electrode gives rise to an anisotropic effective
interaction potential between the particles, with an algebraically long-ranged
in-plane decay. In a comprehensive parameter scan that covers the typical range
of experimentally accessible plasma conditions, we calculate and compare the
mode-coupling predictions for the glass transition in both kinds of systems.Comment: 10 pages, 8 figure
Classical Liquids in Fractal Dimension
We introduce fractal liquids by generalizing classical liquids of integer
dimensions to a fractal dimension . The particles composing
the liquid are fractal objects and their configuration space is also fractal,
with the same non-integer dimension. Realizations of our generic model system
include microphase separated binary liquids in porous media, and highly
branched liquid droplets confined to a fractal polymer backbone in a gel. Here
we study the thermodynamics and pair correlations of fractal liquids by
computer simulation and semi-analytical statistical mechanics. Our results are
based on a model where fractal hard spheres move on a near-critical percolating
lattice cluster. The predictions of the fractal Percus-Yevick liquid integral
equation compare well with our simulation results.Comment: Changed titl
Structural correlations in diffusiophoretic colloidal mixtures with nonreciprocal interactions
Nonreciprocal effective interaction forces can occur between mesoscopic particles in colloidal suspensions that are driven out of equilibrium. These forces violate Newton's third law actio  =  reactio on coarse-grained length and time scales. Here we explore the statistical mechanics of Brownian particles with nonreciprocal effective interactions. Our model system is a binary fluid mixture of spherically symmetric, diffusiophoretic mesoscopic particles, and we focus on the time-averaged particle pair- and triplet-correlation functions. Based on the many-body Smoluchowski equation we develop a microscopic statistical theory for the particle correlations and test it by computer simulations. For model systems in two and three spatial dimensions, we show that nonreciprocity induces distinct nonequilibrium pair correlations. Our predictions can be tested in experiments with chemotactic colloidal suspensions
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