72 research outputs found
Structure and Relaxation Dynamics of a Colloidal Gel
Using molecular dynamics computer simulations we investigate the structural
and dynamical properties of a simple model for a colloidal gel at low volume
fraction. We find that at low T the system is forming an open percolating
cluster, without any sign of a phase separation. The nature of the relaxation
dynamics depends strongly on the length scale/wave-vector considered and can be
directly related to the geometrical properties of the spanning cluster.Comment: 7 pages of EPL-tex; 4 figures, revised versio
Scaling between Structural Relaxation and Particle Caging in a Model Colloidal Gel
In polymers melts and supercooled liquids, the glassy dynamics is
characterized by the rattling of monomers or particles in the cage formed by
their neighbors. Recently, a direct correlation in such systems, described by a
universal scaling form, has been established between the rattling amplitude and
the structural relaxation time. In this paper we analyze the glassy dynamics
emerging from the formation of a persistent network in a model colloidal gel at
very low density. The structural relaxation time of the gel network is compared
with the mean squared displacement at short times, corresponding to the
localization length associated to the presence of energetic bonds.
Interestingly, we find that the same type of scaling as for the dense glassy
systems holds. Our findings well elucidate the strong coupling between the
cooperative rearrangements of the gel network and the single particle
localization in the structure. Our results further indicate that the scaling
captures indeed fundamental physical elements of glassy dynamics.Comment: Submitted to Soft Matter for web theme on ISM
Time-resolved microstructural changes in large amplitude oscillatory shear of model single and double component soft gels
Soft particulate gels can reversibly yield when sufficient deformation is
applied, and the characteristics of this transition can be enhanced or limited
by designing hybrid hydrogel composites. While the microscopic dynamics and
macroscopic rheology of these systems have been studied separately in detail,
the development of direct connections between the two has been difficult,
particularly with regard to the non-linear rheology. To bridge this gap, we
perform a series of large amplitude oscillatory shear (LAOS) numerical
measurements on model soft particulate gels at different volume fractions using
coarse-grained molecular dynamics simulations. We first study a particulate
network with local bending stiffness and then we combine it with a second
component that can provide additional crosslinking to obtain two-component
networks. Through the sequence of physical processes (SPP) framework we define
time-resolved dynamic moduli and, by tracking the changes in these moduli
through the period, we can distinguish transitions in the material behavior as
a function of time. This approach helps us establish the microsopic origin of
the non-linear rheology by connecting the changes in dynamics moduli to the
corresponding microstructural changes during the deformation including the
non-affine displacement of particles, and the breakage, formation, and
orientation of bonds.Comment: 17 pages, 14 figures, submitted to The Journal of Rheolog
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