Figure 8.
Measured and predicted dimensionless diffusivities for colloidal silica in Ludox (a) SM 30, (b) HS 40 and (c) TM 50, at equilibrium salt concentrations of 0.5 mM (lighter, green) and 5 mM (darker, red). The large experimental scatter near ϕ=0.2 is an artefact of numerical differentiation of slowly varying data. Arrows show the first volume fraction where the deviatoric strain, or anisotropy, is measurably non-zero. In other words, it marks the point where the dispersion begins to act as a solid, with a yield stress. In (a), we also show the corresponding prediction (as a dashed line) where equation (2.15) is replaced by the modified hard-sphere compressibility factor ZP from Peppin et al. [9], which diverges at random close packing. Figure data are provided in the electronic supplementary material.