Abstract
We studied the stationary sedimentation profiles of colloidal gels in which the arrested phase separation process is driven by depletion forces, obtained by compressing the samples by either natural or artificial gravity in the range between 6$g$ and 2300$g$. We found that the rheological properties of these gels display a drastic change when the particle volume fraction $\phi$ exceeds a value $\phi_c$ which barely depends on the strength of the attractive forces. The compressive yield stress $\Pi(\phi)$, in fact, first grows as a power law of $\phi$ for $\phi \lesssim \phi_c$ and, then, displays a diverging behavior for larger values of the gel volume fraction, with an asymptotic value similar to the random close packing value for hard spheres. The evidence we collected suggests that $\phi_c$ essentially coincides with the colloid-rich liquid branch of the metastable coexistence line, rather than with an attractive glass line penetrating inside the coexistence region, for which lower $\phi$ values, also dependent on the strength of the interactions, are expected.
Enrico Lattuada
Postdoctoral Researcher
Investigating the structure and dynamics of colloidal systems using optical techniques.