Regulating droplet-surface contact time via a predeposited microparticle

Regulating droplet-surface contact time is a core demand for optimizing performance in inkjet printing, spray cooling, agricultural spraying, and other industrial fields. Conventional strategies relying on surface microstructure modification suffer from high fabrication costs and compromised surface properties. This study investigates the regulation of droplet-surface contact time via a predeposited microparticle in two configurations, while also presenting a numerical coupling of the three-dimensional pseudopotential lattice Boltzmann (LB) method and discrete element method (DEM) to resolve fluid-particle-wall interactions. Results demonstrate that a microparticle predeposited on a superhydrophobic surface extends contact time primarily by expanding the droplet spreading area, achieving a maximum extension of up to ∼40% (depending on the Weber number and particle volume fraction). This effect is enhanced with higher particle volume fraction φ and lower contact angle, as the liquid-particle contact area A_{l-p}^{*} exhibits a linear relationship with spreading time across different Weber numbers. For a particle predeposited within a droplet, the formed particle-laden droplet exhibits a characteristic droplet spreading-particle rebound motion pattern. The inertial stretching effect induced by particle rebound suppresses droplet spreading and accelerates retraction, leading to a significant reduction in contact time (up to ∼20%). This shortening effect is intensified by higher particle volume fraction, density, restitution coefficient, and impact Weber number. Additionally, microparticle predeposition modulates droplet dynamics and deformation, leading to energy conversion and dissipation, thereby reducing the rebound stretching height and preventing droplet breakup. This surface-friendly method provides a high-efficiency and feasible pathway for precise droplet-surface contact time control and offering important theoretical support for the optimization of droplet-related industrial technologies.