Emulsion paints (and a bunch of other things) are basically very small particles suspended in water. When they dry the water evaporates pushing the particles together, and as these particles are soft they then coalesce, forming a film that is the dry coat of paint. By small I mean mostly less than a micrometre, or a thousandth of a millimetre, in diameter. So drying paints are an example of out-of-equilibrium soft matter.
I have an active collaboration with my Surrey colleague Joe Keddie to study these systems. I run the modelling side of the collaboration. We have a recent Phys Rev Lett paper (arXiv) on how during the drying of a liquid film containing big (red in images above) and small (yellow) particles, the particles segregate into layers, with the small ones in the top layer (see in the image on the right). This effect was discovered by a postdoc, Andrea Fortini, who has written a blog post (with movie!) on this work.
The work is described in a news item by the American Physical Society’s news service Physics. It has an embedded movie by Andrea if you want to see the effect happening. There is also a piece on it in the UK’s Institute of Physics’ Physics World. If you prefer the language of Cervantes, you can read the blog post of Francisco Villatoro.