Salt concentration effects on evaporation-driven pattern formation in sessile droplets

Abstract

We report experimental findings on the formation of salt deposits upon the complete evaporation of a sessile droplet containing sodium chloride. We also offer both quantitative and qualitative information to help comprehend the intricate mechanisms underlying the evaporation problem.We propose a mechanism for solutal instability that aligns with our experimental results and literature findings. During the solute crystallization and eventual deposit formation, we observe two phases: the first phase, where crystal growth is absent, spans from the initial time to 65 % of the evaporation duration. The second phase occurs when the chemical process of crystallization sets in. We provide quantitative data on the crystallization process, utilizing the normalized average distance between crystals as a function of relative humidity and initial salt concentration.