Rheology signature of flocculated silica suspensions

We experimentally study the behavior of suspensions of silica particles in aqueous solution. Despite many studies on these materials, the dependence of the overall rheological properties of the suspension on particle size, solid volume fraction, ionic strength, and strain history remains debated. In this paper, we manage to manufacture materials and develop procedures that allow us (i) to approach this problem in the best possible way and (ii) to check that the results obtained with well controlled systems (monodisperse silica spherical particles) also apply to less controlled suspensions (crushed silica particles). We find that the elastic modulus-particle size and yield stress-particle size relationships follow power laws that disagree with classical models from the literature. We also show that elastic modulus versus yields stress data fall on a single master curve when rescaled by particle size, whatever are solid volume fraction, resting time, and ionic strength. This suggests that the rescaled elastic modulus can play the role of a parameter in a structural kinetics model of the behavior of thixotropic suspensions. Furthermore confocal observations of the system provided evidence that the evolution of the overall properties of the material with resting time cannot be ascribed to changes in the particle network.