Deposits from evaporating emulsion drops

Abstract

The processes in which droplets evaporate from solid surfaces, leaving behind distinct deposition patterns, have been studied extensively for variety of solutions. In this work, by combining different microscopy techniques (confocal fluorescence, video and Raman) we investigate pattern formation and evaporation-induced phase change in drying oil-in-water emulsion drops. This combination of techniques allows us to perform drop shape analysis while visualizing the internal emulsion structure simultaneously. We observe that drying of the continuous water phase of emulsion drops on hydrophilic surfaces favors the formation of ring-like zones depleted of oil droplets at the contact line, which originate from geometrical confinement of oil droplets by the meniscus. From such a depletion zone, a “coffee ring” composed of surfactant molecules forms as the water evaporates. On all surfaces drying induces emulsion destabilization by coalescence of oil droplets, commencing at the drop periphery. For hydrophobic surfaces, the coalescence of the oil droplets leads to a uniform oil film spreading out from the initial contact line. The evaporation dynamics of these composite drops indicate that the water in the continuous phase of the emulsion drops evaporates predominantly by diffusion through the vapor, showing no large differences to the evaporation of simple water drops.

Synthesis and Characterization of Dimeric Artesunate Glycerol Monocaprylate Conjugate and Formulation of Nanoemulsion Preconcentrate

“…However, the dimensions of the droplets are in the range of ~200 nm to 2 µm with an average height of ~100 nm, which is much larger than the droplet size found on the mica surface. This is because the silicon wafer is a less polar substrate, and spreading a slightly higher concentration of the sample on the substrate, along with solvent evaporation, leads to the formation of large droplets due to the evaporation-induced coalescence of oil droplets [ 49 ]. A schematic diagram of the coalescence process of the oil droplets during drying on the substrate is shown in Figure 6 b.…”

“…The resultant product was kept under high vacuum to provide D-AS-GC conjugate as white solid. ESI-TOF MS (m/z): calculated for C 49…”

Drying Drops of Colloidal Dispersions

“…Drying drops of emulsions are an example of a multicomponent, multiphase system. For example, when oil-in-water or water-in-oil emulsions are dried (90,91), evaporation-driven flows carry the dispersed droplets to the periphery of the evaporating drop, bringing them close to one another and thus facilitating drop-drop coalescence. On one hand, on a hydrophobic surface, the coalesced oil droplets form an oil layer that spreads beyond the initial contact radius.…”