On the Long-Term Stability of Colloidal Gels

Executive Summary

We summarise the findings of our second three-year project on the long-term stability of colloidal gels. In our first three-year project, we showed that it was processes occurring at the top of gels that appeared to control the way these materials collapsed under gravity, and that simulations without hydrodynamic interactions could not reproduce any of the plethora of observed phenomenology. These findings form the starting points of our second three-year project. First, we use lattice-Boltzmann simulations that take into account hydrodynamic interactions to study a variety of local phenomenology, revealing the subtle but important ways in which such interactions affect gel properties via the kinetics of aggregation. Secondly, experiments show that a curved meniscus gives rise to dense ‘debris’ on the top of gels, precipitating collapse. Eliminating curved menisci, of either sign, significantly increases gel life times. Finally, towards the end of our project, we studied a colloidal gel containing large, non-Brownian particles, mimicking how colloidal gels are used in many industrial formulations. Unexpectedly, we find that the behavior of this system depends on preparation protocol, so that using colloidal gels to suspend large particles introduces complexities that are not revealed by studying the colloidal gels alone.