Drying suspensions often leave behind complex patterns of particulates, as
might be seen in the coffee stains on a table. Here we consider the dynamics of
periodic band or uniform solid film formation on a vertical plate suspended
partially in a drying colloidal solution. Direct observations allow us to
visualize the dynamics of the band and film deposition, and the transition in
between when the colloidal concentration is varied. A minimal theory of the
liquid meniscus motion along the plate reveals the dynamics of the banding and
its transition to the filming as a function of the ratio of deposition and
evaporation rates. We also provide a complementary multiphase model of colloids
dissolved in the liquid, which couples the inhomogeneous evaporation at the
evolving meniscus to the fluid and particulate flows and the transition from a
dilute suspension to a porous plug. This allows us to determine the
concentration dependence of the bandwidth and the deposition rate. Together,
our findings allow for the control of drying-induced patterning as a function
of the colloidal concentration and evaporation rate.Comment: 11 pages, 7 figures, 2 table
