Typical coatings have not one or two, but several species of colloidal particles, and inevitably the particles of each component are not all made with identical diameters but with some spread of diameters. Andrea Fortini and Richard Sear of the consortium studied these effects using computer simulations, and their results have recently been published the American Chemical Society’s Langmuir journal.
They showed that if the mixture contains small, medium and large particles, then if the size differences are sufficiently large, a three-layered structure can be formed in the final dry film. This was in computer simulation, so experiments will be needed to confirm this prediction. The work follows on from consortium work published in 2016. In the structure the top layer is of the small particles, with the medium-sized particles in the middle, and the large particles are in the bottom. This is potentially useful as coatings could be made that spontaneously form a sandwich-like structure during drying.
Their studies of particles with a distribution of diameters likewise found that in the final dry film, the bottom of the film was enriched in the largest particles while the small particles were concentrated at the top. It should be noted that this is not sedimentation, the effect of gravity was not considered in these simulations.