Evaporation Dynamics of Bidispersed Colloidal Suspension Droplets on Hydrophilic Substrates Under Different Relative Humidity and Ambient Temperature

The present work investigates the evaporation of droplets containing bidispersed colloidal particles (0.5 and 1 μm) on hydrophilic glass substrates under different ambient air temperatures (25 and 50 °C) and relative humidity (30, 50 and 70%). Various experimental techniques such as high-speed visualization, 3D profilometry, fluorescence microscopy and SEM microscopy are implemented to study the evaporating droplets. The findings show that by varying the ambient conditions, there exists a significant change in the final deposit patterns and the ring profiles. It is observed that at a given temperature as the Relative Humidity (RH) is increased, the deposit morphology changes from, a thin ring with non-uniform inner deposit to a thick ring with uniform inner deposit. Also, the ring width and height reduced with decreasing RH; moreover, the reduction is more pronounced at higher ambient temperature. These findings suggest possible alteration in the internal flow due to the variation of ambient air temperature and RH. Other aspects, such as sorting of particles near the vicinity of the CL is also investigated. This study is fundamental to understanding the effect of varying ambient conditions in governing the evaporation dynamics of the colloidal suspension droplets and, eventually, the morphology of the final deposition.