Crystallization-Driven Flows within Evaporating Aqueous Saline Droplets

Abstract

Using micro-PIV (Particle Image Velocimetry), we observe for the first time, the direct correlation between crystallisation and hydrodynamics in evaporating micro-litre saline (1M NaCl) sessile drops. The relationship is demonstrated by a remarkable jet of liquid along the base of the drops, induced by and directed at the point of nucleation and subsequent crystal growth. Prior to 2 nucleation the flow is more uniformly outward with the magnitude of the velocity decreasing with time. From calculations and the flow measurements in the two observed stages of evaporation (prior to nucleation and during crystallisation), this jet can be explained on the basis of competition between solutal Marangoni convection and mass-conservation flow. The jet of fluid leads to vortices on either side of the crystal in which the salt concentration is reduced, providing a potential explanation as to why NaCl deposits as a sequence of discrete crystals rather than as a continuous ring for such drops.

A Comprehensive Methodology for Monitoring Evaporitic Mineral Precipitation and Hydrochemical Evolution of Saline Lakes: The Case of Lake Magadi Soda Brine (East African Rift Valley, Kenya)

“…The wetting property of the glass surface and the emerging crystals, and crystallization-driven flow of solutes may control the subsequent patterns after initial nucleation. 35,36 A relatively higher evaporation rate seems responsible for the patterns observed on the center (Figure 1d), creating tiny outward radiating crystals.…”

Effect of Marangoni Convection on the Perovskite Thin Liquid Film Deposition

“…Generally, crystallization or nucleation starts near the triple-phase contact line because evaporation and consequently solute concentration are maximum therein. This problem has been studied on a droplet . The thin-film evaporation and drying process can be similar since both undergo either a high rate of evaporation or a concentration gradient at the triple-phase line with the same triple-phase profile.…”

“…Here, we studied different stages of evaporation and explained a possible analogy between the droplet and thin liquid film. To explore potential relation, we used some cues from the Ristenpart et al and Ajaev et al saline droplet studies to investigate the deposition pattern. Furthermore, wettability, solution concentration, and the substrate pattern for a variety of droplet sizes have shown an imperative impact on the deposition and internal flow patterns.…”

Pattern Formation upon Evaporation of Sessile Droplets of Polyelectrolyte/Surfactant Mixtures on Silicon Wafers

“…They found the formation of volcano-like structures at the center of the deposit. Very recently, Efstratiou et al [ 50 ] found the formation of a rim of evenly spaced salt crystals instead of a continuous rim after the evaporation of aqueous saline droplets. Furthermore, they also found that the type of salt, its initial concentration, and the hydrophilic or hydrophobic character of the substrate can drive the formation of salt deposits with very different morphologies, e.g., continuous rings, concentric rings, or discrete crystals, close to the ring or at the center of the deposit.…”