  Charged colloidal dispersions make up the basis of a broad range of
industrial and commercial products, from paints to coatings and additives in
cosmetics. During drying, an initially liquid dispersion of such particles is
slowly concentrated into a solid, displaying a range of mechanical
instabilities in response to highly variable internal pressures. Here we
summarise the current appreciation of this process by pairing an
advection-diffusion model of particle motion with a Poisson-Boltzmann cell
model of inter-particle interactions, to predict the concentration gradients
around a drying colloidal film. We then test these predictions with osmotic
compression experiments on colloidal silica, and small-angle x-ray scattering
experiments on silica dispersions drying in Hele-Shaw cells. Finally, we use
the details of the microscopic physics at play in these dispersions to explore
how two macroscopic mechanical instabilities -- shear-banding and fracture --
can be controlled.
