Homogeneous nucleation of supersaturated KCl-solutions from single levitated microdroplets

Abstract

Single levitated microdroplets of aqueous potassium chloride (KCl) solutions are investigated as a function of temperature and humidity of their surroundings. Supersaturated solution droplets are obtained from the evaporation of water. The phase transition into solid microparticles is investigated as a function of temperature and humidity, where the experimental conditions favor homogeneous nucleation. The heat of solution of supersaturated KCl-solution droplets containing variable salt concentrations is derived, which is compared to previous results on dilute and saturated KCl-solutions. It is found to be negative, contrary to saturated and dilute solutions. This gives evidence for the formation of KCl clusters in supersaturated solutions prior to nucleation. The rates of homogeneous nucleation from supersaturated KCl solutions are reported, where the temporal evolution of homogeneous nucleation is investigated. Processes occurring on different time scales are identified. These are discussed along with previous works on homogeneous nucleation of pure water and salt solutions.