Colloidal gels made by attractive fractal cluster: Brownian dynamics simulation

Carbon black (CB) suspensions exhibit complex rheological properties, such as yield-stress fluid and thixotropic behaviors. CB consists of rigid fractal aggregates that form agglomerates, leading to a stress-carrying network structure. On the one hand, the gelation and the electrical percolation concentrations are determined by the particle-particle and particle-matrix interaction, and on the other hand, these interactions lead to a multi-scale network structure that results in complex rheo-electric properties. To understand the effect of the microstructure of fractal aggregates on the rheology of CB suspension, we performed Brownian dynamics simulations of fractal clusters. Each fractal cluster consisted of primary particles and maintained its structure during the simulation. The inter-cluster attraction was modeled as the Lennard-Jones interaction between primary particles when they belonged to different clusters. The hydrodynamic interactions between particles were ignored. Here, we present how the cluster structure and attractive interactions affect the scaling law of elasticity versus particle concentration in comparison with colloidal gels made by attractive spheres. The simulation results are also compared with our experimental findings on the effect of solvent quality on the elasticity-conductivity relation. We further explore the shear-induced structures on step-down in the shear-rate tests to explain the experimentally observed thixotropy.