609 research outputs found
Theory of asymmetric non-additive binary hard-sphere mixtures
We show that the formal procedure of integrating out the degrees of freedom
of the small spheres in a binary hard-sphere mixture works equally well for
non-additive as it does for additive mixtures. For highly asymmetric mixtures
(small size ratios) the resulting effective Hamiltonian of the one-component
fluid of big spheres, which consists of an infinite number of many-body
interactions, should be accurately approximated by truncating after the term
describing the effective pair interaction. Using a density functional treatment
developed originally for additive hard-sphere mixtures we determine the zero,
one, and two-body contribution to the effective Hamiltonian. We demonstrate
that even small degrees of positive or negative non-additivity have significant
effect on the shape of the depletion potential. The second virial coefficient
, corresponding to the effective pair interaction between two big spheres,
is found to be a sensitive measure of the effects of non-additivity. The
variation of with the density of the small spheres shows significantly
different behavior for additive, slightly positive and slightly negative
non-additive mixtures. We discuss the possible repercussions of these results
for the phase behavior of binary hard-sphere mixtures and suggest that
measurements of might provide a means of determining the degree of
non-additivity in real colloidal mixtures
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
Rosenfeld functional for non-additive hard spheres
The fundamental measure density functional theory for hard spheres is
generalized to binary mixtures of arbitrary positive and moderate negative
non-additivity between unlike components. In bulk the theory predicts
fluid-fluid phase separation into phases with different chemical compositions.
The location of the accompanying critical point agrees well with previous
results from simulations over a broad range of non-additivities and both for
symmetric and highly asymmetric size ratios. Results for partial pair
correlation functions show good agreement with simulation data.Comment: 8 pages with 4 figure
Coarse-graining strategies in polymer solutions
We review a coarse-graining strategy (multiblob approach) for polymer
solutions in which groups of monomers are mapped onto a single atom (a blob)
and effective blob-blob interactions are obtained by requiring the
coarse-grained model to reproduce some coarse-grained features of the
zero-density isolated-chain structure. By tuning the level of coarse graining,
i.e. the number of monomers to be mapped onto a single blob, the model should
be adequate to explore the semidilute regime above the collapse transition,
since in this case the monomer density is very small if chains are long enough.
The implementation of these ideas has been previously based on a
transferability hypothesis, which was not completely tested against
full-monomer results (Pierleoni et al., J. Chem. Phys, 127, 171102 (2007)). We
study different models proposed in the past and we compare their predictions to
full-monomer results for the chain structure and the thermodynamics in the
range of polymer volume fractions \Phi between 0 and 8. We find that the
transferability assumption has a limited predictive power if a
thermodynamically consistent model is required. We introduce a new tetramer
model parametrized in such a way to reproduce not only zero-density
intramolecular and intermolecular two-body probabilities, but also some
intramolecular three-body and four-body distributions. We find that such a
model correctly predicts three-chain effects, the structure and the
thermodynamics up to \Phi ~ 2, a range considerably larger than that obtained
with previous simpler models using zero-density potentials. Our results show
the correctness of the ideas behind the multiblob approach but also that more
work is needed to understand how to develop models with more effective monomers
which would allow us to explore the semidilute regime at larger chain volume
fractions.Comment: 33 pages, 19 figures, submitted to Soft Matte
Aansprakelijkheidsbeperking van (markt)- toezichthouders
_In dit artikel onderzoeken wij met behulp van inzichten uit de rechtseconomie of
beperking van de aansprakelijkheid van toezichthouders wegens falend toezicht
wenselijk is. Omdat er redenen zijn om te vrezen dat onbeperkte aansprakelijkheid
tot excessief toezicht leidt, betogen wij dat de aansprakelijkheid inderdaad beperkt
moet worden. Deze beperking moet niet bestaan in een maximumbedrag waarvoor
de toezichthouder aansprakelijk kan zijn, maar in een soepeler gedragsstandaard,
zoals âopzet of grove schuldâ.
The Asakura-Oosawa model in the protein limit: the role of many-body interactions
We study the Asakura-Oosawa model in the "protein limit", where the
penetrable sphere radius is much greater than the hard sphere radius
. The phase behaviour and structure calculated with a full many-body
treatment show important qualitative differences when compared to a description
based on pair potentials alone. The overall effect of the many-body
interactions is repulsive.Comment: 9 pages and 11 figures, submitted to J. Phys.: Condensed Matter,
special issue "Effective many-body interactions and correlations in soft
matter
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