The deposition of colloidal particles from a sessile drop of a volatile suspension subject to particle adsorption and coagulation

Electrical double layer and van der Waals (DLVO) forces are known to determine the morphology of the deposit of colloidal particles following the evaporation of the carrier liquid. It is assumed that the adsorption of particles to the solid substrate and their coagulation in the liquid are the mechanisms connecting DLVO forces to the morphology of the deposit. We use theory to test this assertion. We model the deposition of particles from a volatile drop while accounting for the contribution of adhesion and coagulation. The rate of both mechanisms is connected to DLVO forces via the interaction-force boundary layer and the Smoluchowski theorems, respectively. We present analytical solutions for the morphology of the deposit, accounting for particle adsorption and pair-limited coagulation, and a corresponding numerical analysis for the case where particle adhesion and coagulation are concurrent. We conclude that larger aggregates of particles are found near the edge of the drop at the expense of the smaller ones in the absence of adhesion. The adhesion of particles to the substrate smears the deposit, rendering large aggregates to appear near the center of the drop. The analysis is in agreement with a previous experiment when accounting for the corresponding DLVO forces.

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