Kaplan, C. Nadir, Ning Wu, Shreyas Mandre, Joanna Aizenberg, and L. Mahadevan. 2015. “Dynamics of Evaporative Colloidal Patterning.” Phys. Fluids 27 (9) (September): 092105. Portico. doi:10.1063/1.4930283.
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 band and film deposition, where both are made of multiple layers of close packed particles. We further see that there is a transition between banding and filming 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.
Funding: Air Force Office of Scientific Research (AFOSR) under
Award No. FA9550-09-1-0669-DOD35CAP, the Harvard-MRSEC DMR-1420570, and the Kavli
Institute for Bionano Science and Technology at Harvard University.