Resulting deposition patterns in various sessile droplets undergoing evaporation

Evaporation of liquid droplets and the resulting dried-out pattern are important to many applications (such as in paint industries, monument preservation, high-salinity agricultural regions, etc.) and are often associated with the coffee-ring effect in the case of colloidal and suspension droplets; however, the same is not true for saline homogeneous solution droplets. In this study, three different diagnostic techniques, viz. optical imaging, weight measurement, and thermal imaging, were used. Here, we thoroughly investigate the different patterns obtained during the drying of a fixed volume of sessile droplets on the hydrophilic substrate and the effect of evaporation on them. In the case of sodium chloride, isolated and nearly equidistant crystals were formed on the contact line while with heptahydrate magnesium sulfate, a Mikado-like structure was obtained. Using the weight measurement technique, the mass loss rate was found to vary nonlinearly, although the nature of the rate remained the same for salt solutions. Further, experimental data showed that the evaporation and precipitation rates both depend on the type of solution and can be defined in terms of different stages. We aim to extend this study to understand the effect of salt in the drying of soils and other porous media, especially focusing on crystallization and crystal growth.