1,396 research outputs found
Extended Wertheim theory predicts the anomalous chain length distributions of divalent patchy particles under extreme confinement
Colloidal patchy particles with divalent attractive interaction can
self-assemble into linear polymer chains. Their equilibrium properties in 2D
and 3D are well described by Wertheim's thermodynamic perturbation theory which
predicts a well-defined exponentially decaying equilibrium chain length
distribution. In experimental realizations, due to gravity, particles sediment
to the bottom of the suspension forming a monolayer of particles with a
gravitational height smaller than the particle diameter. In accordance with
experiments, an anomalously high monomer concentration is observed in
simulations which is not well understood. To account for this observation, we
interpret the polymerization as taking place in a highly confined quasi-2D
plane and extend the Wertheim thermodynamic perturbation theory by defining
addition reactions constants as functions of the chain length. We derive the
theory, test it on simple square well potentials, and apply it to the
experimental case of synthetic colloidal patchy particles immersed in a binary
liquid mixture that are described by an accurate effective critical Casimir
patchy particle potential. The important interaction parameters entering the
theory are explicitly computed using the integral method in combination with
Monte Carlo sampling. Without any adjustable parameter, the predictions of the
chain length distribution are in excellent agreement with explicit simulations
of self-assembling particles. We discuss generality of the approach, and its
application range.Comment: The following article has been submitted to The Journal of Chemical
Physic
Shear-induced anisotropic decay of correlations in hard-sphere colloidal glasses
Spatial correlations of microscopic fluctuations are investigated via
real-space experiments and computer simulations of colloidal glasses under
steady shear. It is shown that while the distribution of one-particle
fluctuations is always isotropic regardless of the relative importance of shear
as compared to thermal fluctuations, their spatial correlations show a marked
sensitivity to the competition between shear-induced and thermally activated
relaxation. Correlations are isotropic in the thermally dominated regime, but
develop strong anisotropy as shear dominates the dynamics of microscopic
fluctuations. We discuss the relevance of this observation for a better
understanding of flow heterogeneity in sheared amorphous solids.Comment: 6 pages, 4 figure
Yielding and irreversible deformation below the microscale: Surface effects and non-mean-field plastic avalanches
Nanoindentation techniques recently developed to measure the mechanical
response of crystals under external loading conditions reveal new phenomena
upon decreasing sample size below the microscale. At small length scales,
material resistance to irreversible deformation depends on sample morphology.
Here we study the mechanisms of yield and plastic flow in inherently small
crystals under uniaxial compression. Discrete structural rearrangements emerge
as series of abrupt discontinuities in stress-strain curves. We obtain the
theoretical dependence of the yield stress on system size and geometry and
elucidate the statistical properties of plastic deformation at such scales. Our
results show that the absence of dislocation storage leads to crucial effects
on the statistics of plastic events, ultimately affecting the universal scaling
behavior observed at larger scales.Comment: Supporting Videos available at
http://dx.plos.org/10.1371/journal.pone.002041
Colloidal aggregation in microgravity by critical Casimir forces
By using the critical Casimir force, we study the attractive strength
dependent aggregation of colloids with and without gravity by means of Near
Field scattering. Significant differences were seen between microgravity and
ground experiments, both in the structure of the formed fractal aggregates as
well as the kinetics of growth. Ground measurements are severely affected by
sedimentation resulting in reaction limited behavior. In microgravity, a purely
diffusive behavior is seen reflected both in the measured fractal dimensions
for the aggregates as well as the power law behavior in the rate of growth.
Formed aggregates become more open as the attractive strength increases.Comment: 4 pages, 3 figure
Protein microparticles visualize the contact network and rigidity onset in the gelation of model proteins
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