Figure 3.

Poisson–Boltzmann cell model. (a) An electrically neutral spherical cell is constructed around each charged particle. (b) Within this cell, the equilibrium distribution of ions is shown for the example case of colloidal silica with radius a=8 nm and surface charge density σ=0.5 e nm⁻² at volume fraction ϕ=0.05 in equilibrium with a monovalent salt of concentration n₀=5 mM. The ionic concentrations at the outer surface of the cell are related to the osmotic pressure of the dispersion. (c) These colloidal interactions will typically increase the effective diffusivity of the particles, D/D₀, above that of hard spheres (black curve, Z_q=0). Peaking from left to right are shown the cases for (red) a=8 nm, σ=0.5 e nm⁻² and n₀= 5 mM, (green) a=99 nm, σ=0.033 e nm⁻² and n₀=1 mM and (blue) a=99 nm, σ=0.033 e nm⁻² and n₀=5 mM.