821 research outputs found
Microscopic origin of nonlinear non-affine deformation and stress overshoot in bulk metallic glasses
The atomic theory of elasticity of amorphous solids, based on the nonaffine
response formalism, is extended into the nonlinear stress-strain regime by
coupling with the underlying irreversible many-body dynamics. The latter is
implemented in compact analytical form using a qualitative method for the
many-body Smoluchowski equation. The resulting nonlinear stress-strain
(constitutive) relation is very simple, with few fitting parameters, yet
contains all the microscopic physics. The theory is successfully tested against
experimental data on metallic glasses, and it is able to reproduce the
ubiquitous feature of stress-strain overshoot upon varying temperature and
shear rate. A clear atomic-level interpretation is provided for the stress
overshoot, in terms of the competition between the elastic instability caused
by nonaffine deformation of the glassy cage and the stress buildup due to
viscous dissipation.Comment: Physical Review B Rapid Comm., in pres
Approximate analytical description of the nonaffine response of amorphous solids
An approximation scheme for model disordered solids is proposed that leads to
the fully analytical evaluation of the elastic constants under explicit account
of the inhomogeneity (nonaffinity) of the atomic displacements. The theory is
in quantitative agreement with simulations for central-force systems and
predicts the vanishing of the shear modulus at the isostatic point with the
linear law {\mu} ~ (z - 2d), where z is the coordination number. The vanishing
of rigidity at the isostatic point is shown to be a consequence of the
canceling out of positive affine and negative nonaffine terms
Shear-driven solidification of dilute colloidal suspensions
We show that the shear-induced solidification of dilute charge-stabilized
(DLVO) colloids is due to the interplay between the shear-induced formation and
breakage of large non-Brownian clusters. While their size is limited by
breakage, their number density increases with the shearing-time. Upon flow
cessation, the dense packing of clusters interconnects into a rigid state by
means of grainy bonds, each involving a large number of primary colloidal
bonds. The emerging picture of shear-driven solidification in dilute colloidal
suspensions combines the gelation of Brownian systems with the jamming of
athermal systems
Nonequilibrium free energy of colloidal glasses under shear
The free energy of hard-sphere systems provides a direct link between the particle-scale structure and macroscopic thermodynamic properties. Here, we employ this framework to investigate the shear-induced structure of a colloidal glass, and link it to its macroscopic mechanical and thermodynamic state. We measure the nonequilibrium free energy under shear from the free volumes of the particles, and monitor its evolution with the applied strain. Unlike crystals, for which the elastic energy increases quadratically with strain due to affine particle displacements, for glasses the free energy decreases due to non-affine displacements and dissipation, reflecting the ability of the glass to reach deeper free-energy minima. We model this decrease using the nonaffine shear modulus and a standard viscous dissipative term. Our model and measurements allow us to disentangle the complex contributions of affine and nonaffine particle displacements in the transient shear deformation of glasses
Shear-induced reaction-limited aggregation kinetics of Brownian particles at arbitrary concentrations
The aggregation of interacting Brownian particles in sheared concentrated
suspensions is an important issue in colloid and soft matter science per se.
Also, it serves as a model to understand biochemical reactions occurring in
vivo where both crowding and shear play an important role. We present an
effective medium approach within the Smoluchowski equation with shear which
allows one to calculate the encounter kinetics through a potential barrier
under shear at arbitrary colloid concentrations. Experiments on a model
colloidal system in simple shear flow support the validity of the model in the
range considered. By generalizing Kramers' rate theory to the presence of
collective hydrodynamics, our model explains the significant increase in the
shear-induced reaction-limited aggregation kinetics upon increasing the colloid
concentration
Elasticity of arrested short-ranged attractive colloids: homogeneous and heterogeneous glasses
We evaluate the elasticity of arrested short-ranged attractive colloids by
combining an analytically solvable elastic model with a hierarchical arrest
scheme into a new approach, which allows to discriminate the microscopic
(primary particle-level) from the mesoscopic (cluster-level) contribution to
the macroscopic shear modulus. The results quantitatively predict experimental
data in a wide range of volume fractions and indicate in which cases the
relevant contribution is due to mesoscopic structures. On this basis we propose
that different arrested states of short-ranged attractive colloids can be
meaningfully distinguished as homogeneous or heterogeneous colloidal glasses in
terms of the length-scale which controls their elastic behavior.Comment: 3 figures, revised version, to appear in Physical Review Letter
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