Particle capturing via droplet impact on superhydrophobic mesh.

Abstract

<h4>Hypothesis</h4>Open-chip droplet-based microreactors are continually finding newer applications, spanning areas such as drug discovery and materials exploration through combinatorial chemistry. The incorporation of small quantities of particulate inclusions into these droplets holds significant potential for enhancing their functionalities, but remains challenged due to the inherent lack of precise control. We hypothesize that this limitation can be addressed by leveraging the jet formed during the controlled impact of a falling droplet on a superhydrophobic mesh, enabling precise capture of particulates from a strategically positioned bed beneath the mesh.<h4>Experiments</h4>Controlled experiments were performed to investigate the droplet impingement on a superhydrophobic mesh. High-speed imaging was employed to analyze the dynamics of the resulting jet and its interaction with the particle housing beneath the mesh, revealing the intricacies of the particle capture process. Specific strategies were implemented to tune the droplet energy and assess the impact of the distance between the mesh and the particle housing. The effects of particulate properties and medium rheology were examined through extensive experiments using dissolvable dye particles, insoluble glass beads, highly viscous liquids, and low surface tension liquids.<h4>Findings</h4>Our results unveiled highly selective configurations that enabled tunable capture of microparticles across a wide range of volumetric compositions, spanning over three orders of magnitude in the particle numbers in a given droplet volume (∼10 to ∼2000). These also demonstrated the successful pickup of nanoscale dye particles from trace amounts (sub-microgram) of samples, which is otherwise challenging to achieve. The versatility of the method was further exemplified by its ability to capture particles in a highly viscous medium (58 mPa·s) and also low surface tension (33.67 mN/m). These findings are expected to drive advancements in a wide variety of applications, ranging from biomedical analysis to the synthesis of specialized materials for drug discovery, where precise capturing and encapsulation of particles of a wide variety of sizes and concentrations are imperative.