Abstract
We have investigated the stationary sedimentation profiles of colloidal gels obtained by an arrested phase-separation process driven by depletion forces, which have been compressed either by natural gravity or by a centrifugal acceleration ranging between 6$g$ and 2300$g$. Our measurements show that the gel rheological properties display a drastic change when the gel particle volume fraction exceeds a value $\phi_c$, which barely depends on the strength of the interparticle attractive forces that consolidate the network. In particular, the gel compressive yield stress $\Pi(\phi)$, which increases as $\Pi(\phi) \sim \phi^{4.2}$ for $ \phi \lesssim \phi_c$, displays a diverging behaviour for $\phi>\phi_c$, with an asymptotic value that is close to the random close packing value for hard spheres. The evidence we obtained suggests that $\phi_c$ basically coincides with the liquid (colloid-rich) branch of the metastable coexistence curve, rather than with the lower (and $\phi$-dependent) values expected for an attractive glass line penetrating inside the coexistence region.
Enrico Lattuada
Postdoctoral Researcher
Investigating the structure and dynamics of colloidal systems using optical techniques.