Wettability Effect on Evaporation Dynamics and Crystalline Patterns of Sessile Saline Droplets.

The evaporative dynamics and crystalline patterns from sessile saline droplets on various substrates are experimentally investigated. On the silicon wafer and poly(methyl methacrylate) (PMMA) plate, the saline droplets exhibit unique evaporative dynamics such that the contact angle keeps increasing for a lasting period. Such an enlargement in contact angle is attenuated at a higher salt concentration. Interestingly, the onset of precipitation is almost overlapped with the end of contact angle enlargement when the contact angle reaches its apex. The lower wettability and the smaller pinning effect of silicon wafer and PMMA result in the morphology of crystalline cubes at the droplet center. On the soda lemon glass, the high wettability and lifetime pinning stage of the droplet lead to spherical profiles of precipitation. The crystalline deposit depends on the salt concentration on soda lemon glass such that it is comprised of exterior cracked layers of salt and interior separated small cubes for low salt concentrations, whereas large crystalline chunks stay near the droplet rim for high salt concentrations.