269 research outputs found
On the possibility of extending the Nore-Frenkel generalized law of correspondent states to non-isotropic patchy interactions
Colloidal systems (and protein solutions) are often characterized by
attractive interactions whose range is much smaller than the particle size.
When this is the case and the interaction is spherical, systems obey a
generalized law of correspondent states (GLCS), first proposed by Noro and
Frenkel [ J.Chem.Phys. 113, 2941 (2000) ]. The thermodynamic properties become
insensitive to the details of the potential, depending only on the value of the
second virial coefficient B_2 and the density . The GLCS does not
generically hold for the case of non-spherical potentials. In this Letter we
suggest that when particles interact via short-ranged small-angular amplitude
patchy interactions (so that the condition of only one bond per patch is
fulfilled) it is still possible to generalize the GLCS close to the liquid-gas
critical point. Keywords: Colloids, Second Virial Coefficient, Proteins
interactions, Short-ranged attractive attractions.Comment: 11 pages, 3 figures. Accepted for publication on J. Phys. Chem.
Persistent memory in athermal systems in deformable energy landscapes
We show that memory can be encoded in a model amorphous solid subjected to
athermal oscillatory shear deformations, and in an analogous spin model with
disordered interactions, sharing the feature of a deformable energy landscape.
When these systems are subjected to oscillatory shear deformation, they retain
memory of the deformation amplitude imposed in the training phase, when the
amplitude is below a "localization" threshold. Remarkably, multiple,
persistent, memories can be stored using such an athermal, noise-free,
protocol. The possibility of such memory is shown to be linked to the presence
of plastic deformations and associated limit cycles traversed by the system,
which exhibit avalanche statistics also seen in related contexts.Comment: 5 pages, 4 figure
Effective forces in square well and square shoulder fluids
We derive an analytical expression for the effective force between a pair of
macrospheres immersed in a sea of microspheres, in the case where the
interaction between the two unlike species is assumed to be a square well or a
square shoulder of given range and depth (or height). This formula extends a
similar one developed in the case of hard core interactions only. Qualitative
features of such effective force and the resulting phase diagram are then
analyzed in the limit of no interaction between the small particles.
Approximate force profiles are then obtained by means of integral equation
theories (PY and HNC) combined with the superposition approximation and
compared with exact ones from direct Monte Carlo simulations.Comment: 34 page
Hydrodynamics and the fluctuation theorem
The fluctuation theorem is a pivotal result of statistical physics. It
quantifies the probability of observing fluctuations which are in violation of
the second law of thermodynamics. More specifically, it quantifies the ratio of
the probabilities of observing entropy-producing and entropy-consuming
fluctuations measured over a finite volume and time span in terms of the rate
of entropy production in the system, the measurement volume and time. We study
the fluctuation theorem in computer simulations of planar shear flow. The
simulations are performed employing the method of multiparticle collision
dynamics which captures both thermal fluctuations and hydrodynamic
interactions. The main outcome of our analysis is that the fluctuation theorem
is verified at any averaging time provided that the measurement volume exhibits
a specific dependence on a hydrodynamic time scale.Comment: 4 pages, 3 figures, to appear on Physical Review Letter
Oscillatory athermal quasi-static deformation of a model glass
We report computer simulations of oscillatory athermal quasi-static shear
deformation of dense amorphous samples of a three dimensional model glass
former. A dynamical transition is observed as the amplitude of the deformation
is varied: for large values of the amplitude the system exhibits diffusive
behavior and loss of memory of the initial conditions, whereas localization is
observed for small amplitudes. Our results suggest that the same kind of
transition found in driven colloidal systems is present in the case of
amorphous solids (e.g. metallic glasses). The onset of the transition is shown
to be related to the onset of energy dissipation. Shear banding is observed for
large system sizes, without, however, affecting qualitative aspects of the
transition
Aging in short-ranged attractive colloids: A numerical study
We study the aging dynamics in a model for dense simple liquids, in which
particles interact through a hard-core repulsion complemented by a short-ranged
attractive potential, of the kind found in colloidal suspensions. In this
system, at large packing fractions, kinetically arrested disordered states can
be created both on cooling (attractive glass) and on heating (repulsive glass).
The possibility of having two distinct glasses, at the same packing fraction,
with two different dynamics offers the unique possibility of comparing --
within the same model -- the differences in aging dynamics. We find that, while
the aging dynamics of the repulsive glass is similar to the one observed in
atomic and molecular systems, the aging dynamics of the attractive glass shows
novel unexpected features.Comment: 8 pages, 11 figures, submited to Journal of Chemical Physic
Mode-Coupling Theory of Colloids with Short-range Attractions
Within the framework of the mode-coupling theory of super-cooled liquids, we
investigate new phenomena in colloidal systems on approach to their glass
transitions. When the inter-particle potential contains an attractive part,
besides the usual repulsive hard core, two intersecting liquid-glass transition
lines appear, one of which extends to low densities, while the other one, at
high densities, shows a re-entrant behaviour. In the glassy region a new type
of transition appears between two different types of glasses. The complex
phenomenology can be described in terms of higher order glass transition
singularities. The various glass phases are characterised by means of their
viscoelastic properties. The glass driven by attractions has been associated to
particle gels, and the other glass is the well known repulsive colloidal glass.
These correspondences, in associations with the new predictions of glassy
behaviour mean that such phenomena may be expected in colloidal systems with,
for example, strong depletion or other short-ranged attractive potentials.Comment: 17 pages, 8 figure
Configurational entropy of hard spheres
We numerically calculate the configurational entropy S_conf of a binary
mixture of hard spheres, by using a perturbed Hamiltonian method trapping the
system inside a given state, which requires less assumptions than the previous
methods [R.J. Speedy, Mol. Phys. 95, 169 (1998)]. We find that S_conf is a
decreasing function of packing fraction f and extrapolates to zero at the
Kauzmann packing fraction f_K = 0.62, suggesting the possibility of an ideal
glass-transition for hard spheres system. Finally, the Adam-Gibbs relation is
found to hold.Comment: 10 pages, 6 figure
- âŠ