In recent decades, the recurrence of respiratory infectious diseases, represented by COVID-19, has highlighted the urgency of deeply understanding the mechanisms of droplet transmission. Exhaled droplets, depending on their size, either evolve into aerosols suspended in the air or rapidly settle onto various surfaces under gravity. Although existing research has largely focused on the airborne dynamics of droplets, their physical behavior after deposition on a surface—particularly the mechanisms when a droplet lands on an immiscible sessile droplet to form a 'compound droplet'—remains to be fully elucidated. Focusing on this scenario, this study systematically investigates the morphological evolution and evaporation dynamics of such compound droplets by combining experimental observation, numerical simulation, and theoretical analysis. The study reveals the unique initial configurations and dynamic evolution patterns of compound droplets, and clarifies their evaporation modes, which are significantly different from those of single-component droplets. This research aims to uncover the core physical mechanisms of compound droplet evaporation, providing a crucial theoretical basis for accurately assessing virus viability on contaminated surfaces, optimizing disinfection strategies, and constructing more precise disease transmission models.
 

Compound droplet, Droplet transmission, Evaporation, Interfacial phenomena, Numerical simulation, Virus control