Evaporation Dynamics of Completely Pinned and Partially Pinned Sessile Droplets in Multidroplet Configurations

The evaporation of sessile droplets placed in close proximity is influenced by complex vapor-vapor interactions, producing a shielding effect that can significantly extend droplet lifetimes. This study presents a systematic experimental investigation of evaporation dynamics in multidroplet configurations under ambient conditions, comparing completely pinned and partially pinned contact line modes. Completely pinned droplets are generated by introducing alumina nanoparticles, while partially pinned droplets consist of pure water. An isolated droplet is compared with arrays of two, three, and five droplets, each arranged at a fixed spacing ratio. High-speed shadowgraphy is used to measure droplet height, contact angle, volume, and lifetime. Results show that, although completely pinned droplets evaporate faster in absolute terms due to a constant contact radius, they experience a more pronounced relative lifetime increase from vapor shielding than partially pinned droplets. In five-droplet configurations, lifetimes increase by up to 89 and 124% compared to isolated droplets for partially pinned and completely pinned modes, respectively. A theoretical model incorporating evaporative cooling predicts central droplet lifetimes with good agreement. These findings underscore the coupled influence of contact line mobility and droplet proximity on evaporation rates.