Colloidal gels have a wide range of application, e.g., personal care products, pesticides, and oil-drilling muds. Such gels consist of solid particles that form a system-spanning, stress-baring network, which is able to hold... [ view full abstract ]
Colloidal gels have a wide range of application, e.g., personal care products, pesticides, and oil-drilling muds. Such gels consist of solid particles that form a system-spanning, stress-baring network, which is able to hold the gel up against gravity, when there is a mismatch between the density of the liquid and solid phase. However, the gel is intrinsically unstable and will eventually collapse under the influence of gravity. Understanding this process from a fundamental perspective offers opportunities for improving the stability of colloidal gels.
In this presentation, we study the collapse of a model colloidal gel using lattice-Boltzmann (LB) simulations to explain recent experimental observations of a fast collapse regime [1]. We first demonstrate that including fluid flow using the LB algorithm leads to the formation of thinner and weaker gels in the absence of gravity, compared to simulations where hydrodynamic and hydrostatic effects are not accounted for. This result is similar to to that of Refs. [2,3] and thus gives confidence in our method. We then go beyond the formation process and show that including fluid flow significantly speeds up gel collapse, by a factor that is comparable to the one found in our recent experiments. We further relate the resistance of the gel against gravity to the gravitational Péclet number of the particles. Finally, we demonstrate that introducing hydrodynamics in the simulation can also reproduce the presence of volcano-like objects at the interface between the gel and liquid, as observed in the experiment.
Our analysis shows the importance of hydrodynamic interactions to the dynamic properties of colloidal gels and provides new understanding that has strong implications for improving real-world applications of gels.
[1] R. Harich, T.W. Blythe, M. Hermes, E. Zaccarelli, A.J. Sederman, L.F. Gladden, and W.C.K. Poon, Soft Matter 12, 4300 (2016).
[2] Z. Varga, G. Wang, and J. Swan, Soft Matter 11, 9009 (2015).
[3] Z. Varga and J. Swan, Soft Matter 12, 7670 (2016).
