The Interplay of Spreading, Imbibition and Evaporation for Sessile Droplets on Mesoporous Substrates

We study the dynamics of a droplet that is deposited on a nanoporous silicon substrate with a mean pore diameter of 7 nm. The dynamics results from the combination of three phenomena: spreading, imbibition and evaporation. Here, the evolution of the droplet volume is analyzed, thereby accounting for evaporation of the liquid and its imbibition into the porous substrate. We use water to illustrate the case of the evaporation-dominated regime [1], while squalene, a nearly nonvolatile hydrocarbon, is used to study the imbibition-dominated regime. The experimental results are compared with theoretical results obtained with a mesoscopic hydrodynamic model that is based on a gradient dynamics formulation and takes all three processes into account. The resulting good agreement between the experimental and theoretical results allows us to deepen our understanding of the structure of electrochemically synthesized porous silicon substrates and provides new insights into the fundamentals of fluid transport in nanoporous media.

[1] Seker, E., et al. Kinetics of capillary wetting in nanoporous films in the presence of surface evaporation in Applied Physics Letters, 2008