122 research outputs found
Effective interaction between star polymers
The distance-resolved effective interaction between two star polymers in a
good solvent is calculated by Molecular Dynamics computer simulations. The
results are compared with a pair potential proposed recently by Likos et al.
[Phys. Rev. Lett. 1998, 80, 4450] which is exponentially decaying for large
distances and crosses over, at the corona diameter of the star, to an ultrasoft
logarithmic repulsion for small distances. Excellent agreement is found in a
broad range of star arm numbers.Comment: final version as published, 9 pages + 5 ps-figure
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
Fluid and solid phases of the Gaussian core model
We study the structural and thermodynamic properties of a model of point
particles interacting by means of a Gaussian pair potential first introduced by
Stillinger [Stillinger F H 1976 J. Chem. Phys. 65, 3968]. By employing integral
equation theories for the fluid state and comparing with Monte Carlo simulation
results, we establish the limits of applicability of various common closures
and examine the dependence of the correlation functions of the liquid on the
density and temperature. We employ a simple, mean-field theory for the high
density domain of the liquid and demonstrate that at infinite density the
mean-field theory is exact and that the system reduces to an `infinite density
ideal gas', where all correlations vanish and where the hypernetted chain (HNC)
closure becomes exact. By employing an Einstein model for the solid phases, we
subsequently calculate quantitatively the phase diagram of the model and find
that the system possesses two solid phases, face centered cubic and body
centered cubic, and also displays reentrant melting into a liquid at high
densities. Moreover, the system remains fluid at all densities when the
temperature exceeds 1% of the strength of the interactions.Comment: 22 pages, 10 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
Triplet forces between star polymers
We analyze the effective triplet interactions between the centers of star
polymers in a good solvent. Using an analytical short distance expansion
inspired by scaling theory, we deduce that the triplet part of the three-star
force is attractive but only 11% of the pairwise part even for a close approach
of three star polymers. We have also performed extensive computer simulations
for different arm numbers to extract the effective triplet force. The
simulation data show good correspondence with the theoretical predictions. Our
results justify the effective pair potential picture even beyond the star
polymer overlap concentration.Comment: 14 pages, 5 figure
Nonequilibrium thermodynamics versus model grain growth: derivation and some physical implications
Nonequilibrium thermodynamics formalism is proposed to derive the flux of
grainy (bubbles-containing) matter, emerging in a nucleation growth process.
Some power and non-power limits, due to the applied potential as well as owing
to basic correlations in such systems, have been discussed. Some encouragement
for such a discussion comes from the fact that the nucleation and growth
processes studied, and their kinetics, are frequently reported in literature as
self-similar (characteristic of algebraic correlations and laws) both in basic
entity (grain; bubble) size as well as time scales.Comment: 8 pages, 1 figur
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