Modeling Electrosprayed Particle Assembly on Geometrically Controlled Sessile Droplet Surfaces through Brownian Dynamics Simulations*

Interfacial assembly of colloidal particles holds significant potential for advancing the additive manufacture of thin film materials. Nevertheless, many fundamental questions remain regarding the dynamics of particles and the evolution of monolayer structures confined at the interface. In this study, we utilize electrospray atomization as a nonintrusive method to deliver colloidal particles to geometrically controlled sessile droplets, enabling the creation of colloidal monolayers at the droplet surface. The distinctive feature of electrospray is its ability to impart a substantial electric charge to both the sprayed particles and the receiving substrate. Consequently, the dynamics and assembly of particles can be controlled by electrostatic interactions among the particles themselves and between particles and the substrate. To simulate the impact of these electrostatic interactions on the assembly structure, we combine a mesh-constrained Brownian dynamics algorithm with ANSYS electric field simulations to model particle movement on nonparameterizable surfaces. Consistent with previous experimental observations, our simulations predict the presence of a particle-depletion region near the droplet contact line, arising from long-range electrostatic repulsion between particles and the substrate. Our investigation systematically quantifies the influence of particle and substrate surface charge on assembly structures and the development of the depletion region. Additionally, we also probed the formation of rounded assembly boundaries observed in experiments. These results provide valuable insights into the interplay among various electrostatic interactions during the interfacial assembly of electrosprayed particles.