392 research outputs found
Short-time rotational diffusion in monodisperse charge-stabilized colloidal suspensions
We investigate the combined effects of electrostatic interactions and
hydrodynamic interactions on the short-time rotational self-diffusion
coefficient in charge-stabilized suspensions. We calculate this coefficient as
a function of volume fraction for various effective particle charges and
amounts of added electrolyte. The influence of the hydrodynamic interactions on
the rotational diffusion coefficient is less pronounced for charged particles
than for uncharged ones. Salt-free suspensions are weakly influenced by
hydrodynamic interactions. For these strongly correlated systems we obtain a
quadratic volume fraction-dependence of the diffusion coefficient, which is
well explained in terms of an effective hard sphere model.Comment: 21 pages, LaTeX, 7 Postscript figures included using epsf, to appear
in Physica
Aggregation of self-propelled colloidal rods near confining walls
Non-equilibrium collective behavior of self-propelled colloidal rods in a
confining channel is studied using Brownian dynamics simulations and dynamical
density functional theory. We observe an aggregation process in which rods
self-organize into transiently jammed clusters at the channel walls. In the
early stage of the process, fast-growing hedgehog-like clusters are formed
which are largely immobile. At later stages, most of these clusters dissolve
and mobilize into nematized aggregates sliding past the walls.Comment: 5 pages, 4 figure
Electrokinetic and hydrodynamic properties of charged-particles systems: From small electrolyte ions to large colloids
Dynamic processes in dispersions of charged spherical particles are of
importance both in fundamental science, and in technical and bio-medical
applications. There exists a large variety of charged-particles systems,
ranging from nanometer-sized electrolyte ions to micron-sized charge-stabilized
colloids. We review recent advances in theoretical methods for the calculation
of linear transport coefficients in concentrated particulate systems, with the
focus on hydrodynamic interactions and electrokinetic effects. Considered
transport properties are the dispersion viscosity, self- and collective
diffusion coefficients, sedimentation coefficients, and electrophoretic
mobilities and conductivities of ionic particle species in an external electric
field. Advances by our group are also discussed, including a novel
mode-coupling-theory method for conduction-diffusion and viscoelastic
properties of strong electrolyte solutions. Furthermore, results are presented
for dispersions of solvent-permeable particles, and particles with non-zero
hydrodynamic surface slip. The concentration-dependent swelling of ionic
microgels is discussed, as well as a far-reaching dynamic scaling behavior
relating colloidal long- to short-time dynamics
Colloidal glass transition: Beyond mode-coupling theory
A new theory for dynamics of concentrated colloidal suspensions and the
colloidal glass transition is proposed. The starting point is the memory
function representation of the density correlation function. The memory
function can be expressed in terms of a time-dependent pair-density correlation
function. An exact, formal equation of motion for this function is derived and
a factorization approximation is applied to its evolution operator. In this way
a closed set of equations for the density correlation function and the memory
function is obtained. The theory predicts an ergodicity breaking transition
similar to that predicted by the mode-coupling theory, but at a higher density.Comment: to be published in PR
Non-monotonic density dependence of the diffusion of DNA fragments in low-salt suspensions
The high linear charge density of 20-base-pair oligomers of DNA is shown to
lead to a striking non-monotonic dependence of the long-time self-diffusion on
the concentration of the DNA in low-salt conditions. This generic non-monotonic
behavior results from both the strong coupling between the electrostatic and
solvent-mediated hydrodynamic interactions, and from the renormalization of
these electrostatic interactions at large separations, and specifically from
the dominance of the far-field hydrodynamic interactions caused by the strong
repulsion between the DNA fragments.Comment: 4 pages, 2 figures. Physical Review E, accepted on November 24, 200
Rotational and translational self-diffusion in concentrated suspensions of permeable particles
In our recent work on concentrated suspensions of uniformly porous colloidal
spheres with excluded volume interactions, a variety of short-time dynamic
properties were calculated, except for the rotational self-diffusion
coefficient. This missing quantity is included in the present paper. Using a
precise hydrodynamic force multipole simulation method, the rotational
self-diffusion coefficient is evaluated for concentrated suspensions of
permeable particles. Results are presented for particle volume fractions up to
45%, and for a wide range of permeability values. From the simulation results
and earlier results for the first-order virial coefficient, we find that the
rotational self-diffusion coefficient of permeable spheres can be scaled to the
corresponding coefficient of impermeable particles of the same size. We also
show that a similar scaling applies to the translational self-diffusion
coefficient considered earlier. From the scaling relations, accurate analytic
approximations for the rotational and translational self-diffusion coefficients
in concentrated systems are obtained, useful to the experimental analysis of
permeable-particle diffusion. The simulation results for rotational diffusion
of permeable particles are used to show that a generalized
Stokes-Einstein-Debye relation between rotational self-diffusion coefficient
and high-frequency viscosity is not satisfied.Comment: 4 figure
Enhanced structural correlations accelerate diffusion in charge-stabilized colloidal suspensions
Theoretical calculations for colloidal charge-stabilized and hard sphere
suspensions show that hydrodynamic interactions yield a qualitatively different
particle concentration dependence of the short-time self-diffusion coefficient.
The effect, however, is numerically small and hardly accessible by conventional
light scattering experiments. Applying multiple-scattering decorrelation
equipment and a careful data analysis we show that the theoretical prediction
for charged particles is in agreement with our experimental results from
aqueous polystyrene latex suspensions.Comment: 1 ps-file (MS-Word), 14 page
Self-diffusion coefficients of charged particles: Prediction of Nonlinear volume fraction dependence
We report on calculations of the translational and rotational short-time
self-diffusion coefficients and for suspensions of
charge-stabilized colloidal spheres. These diffusion coefficients are affected
by electrostatic forces and many-body hydrodynamic interactions (HI). Our
computations account for both two-body and three-body HI. For strongly charged
particles, we predict interesting nonlinear scaling relations and depending on volume fraction
, with essentially charge-independent parameters and . These
scaling relations are strikingly different from the corresponding results for
hard spheres. Our numerical results can be explained using a model of effective
hard spheres. Moreover, we perceptibly improve the known result for of
hard sphere suspensions.Comment: 8 pages, LaTeX, 3 Postscript figures included using eps
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