Probing Colloidal Assembly on Non-Axisymmetric Droplet Surfaces via Electrospray

Nanoparticles adsorbed to the surface of a spherical, sessile drop will form an unstructured deposit upon evaporation. When the surface flow is suppressed, particle motion at the interface is random and disordered. To investigate the influence of evaporative flow and capillary interactions on interfacial particle assembly, we created non-spherical droplets using substrate patterning and delivered microparticles to the interface with electrospray atomization. The contact line of the droplet was fixed throughout evaporation, resulting in convection towards sharp corners where the contact angle was lower. Additionally, the non-spherical droplet shape created regions of higher deviatoric curvature where particles assembled via capillary effects. When the particle density on the interface was low, there was a strong convective flow, driving individual particles toward the corners. For higher particle densities, the convective flow was reduced, allowing the particles to assemble into large, ordered monolayers over the course of evaporation. Our findings suggest that the relative influence of evaporative-driven flow and particle interactions can be exploited to build particle monolayers with controllable patterns.