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