Simulations of the dynamic deposition of colloidal particles from a volatile sessile drop.

Hypothesis: The deposition of particles from a volatile liquid drop atop a substrate is primarily governed by the advection and diffusion of the particles in the liquid. Colloidal particles may further coagulate and adsorb to the substrate during the deposition process. The external geometry and the internal composition of the particulate deposit are then determined by an interplay between these four mechanisms.

Simulation: We simulate the process of deposition by solving the governing transport equations. We explore the interplay between the different mechanisms mentioned above. In particular, we study the contribution of the diffusion of colloidal particles and aggregates to the morphology of the deposit, which was neglected in a previous study.

Findings: The rates of diffusion and coagulation of each specific aggregate are dependent on its size. Hence, the transport equation uniquely correlates to each population of aggregates. The overall transport problem, alongside the rates of particle and aggregate adsorption and liquid evaporation, determines the geometry of the deposit. Moreover, the local rate of particle coagulation determines the internal composition of the different aggregate populations in the deposit. Our results appear to be in qualitative agreement with previous experimental findings.