Exploiting droplet impact-driven flows and jetting to guide and extract particles from particle-laden droplets

The low concentration of target particles in liquids necessitates their enrichment to a measurable level to provide precise and accurate analytical results. However, the enrichment and extraction of the adsorbed target particles from the droplets remains a challenge. The existing stimuli-responsive strategies for particle enrichment and extraction are not always desirable, as they depend on various parameters, including charge, dielectric constant, magnetic state, size of the particles, etc., which limits their applicability. An ideal method should be capable of extracting particles from the target droplet, irrespective of particle properties, and the process should be fast, preferably in an additive and electrode-free environment. This article presents an efficient strategy for realizing particle extraction based on droplet impact-driven fluid flows under isothermal, non-evaporative, and additive/electrode-free environments. The process relies on the droplet impact-driven redistribution of the particles at the liquid-air interface and the generation of a particle-rich satellite droplet at a designed Weber number, We similar to 65. The impact dynamics and flow profiles are investigated using simulation and high-speed imaging, and the droplet impact-driven particle extraction is demonstrated experimentally. The particle extraction efficiency is estimated by weight percentage and optical profilometry analysis, and at optimal impact conditions, an extraction efficiency of about 90% is achieved, which takes only a few milliseconds to complete. The role of particle size, surface tension, and We on the extraction efficiency is investigated experimentally. Since the developed method is based on flows, it could be a potential candidate for the extraction/enrichment of various particles/biological entities and does not require complicated setups/skills.