Colloidal assembly on the surface of drying sessile droplets*

The self-assembly of nano or microparticles on evaporating liquid droplets is an important transport process underpinning various applications, such as printing and surface patterning. By applying a recently developed lattice Boltzmann-Brownian Dynamics (LB-BD) method, we observe the aggregation of colloidal particles on the droplet surface for strong particle-fluid interactions. The effective attraction between particles is probed in detail and shows long-range nature. By simulating drying droplets with different geometries, we find that the aggregation spots relate to the local curvature. This indicates that the effective attraction in the simulation resembles the capillary interaction, which is induced by the disturbance of the fluid interface. In addition, we model the particle assembly under evaporation to reveal the interplay of the long-range particle attraction and the evaporation-induced flow field. Our study aims to provide greater insight into the capillary-like assembly of particles in evaporating liquid masses and its relationship to the final deposit.