Evaporation induced destabilization of oil-in-water Pickering emulsions.

HYPOTHESIS

Emulsions are widely used in commercial products such as cosmetics, paints, and adhesives. These products are often used as coating layers where drying of the volatile component is inevitable. The evaporation of volatile components during the drying of the emulsion causes the dispersed droplets to compress against each other, as well as the receding air-solvent interface, resulting in the destabilization of dispersed droplets.

EXPERIMENTS

In this work, we present the evaporation-induced destabilization of a single and multiple Pickering oil droplets stabilized by hematite nanoellipsoids. The contraction of the air-water interface due to the evaporation of water leads to the vertical compression of the oil droplets. In response to the compression, the droplet flattens in the direction of the compression and expands laterally, ultimately leading to bursting.

FINDINGS

The area expansion of the oil droplet under compression shows a non-linear behavior and is independent of the initial droplet size. The droplet flattening, however, increases with increasing droplet size. The maximum lateral expansion of the droplet before bursting is found to be independent of the initial droplet size. A morphological investigation of the particulate film at the droplet surface revealed the nucleation of cracks in the lateral surface as the droplet area expands beyond a critical threshold. The cracks propagate towards the top and bottom surface of the droplet under compression as the expansion increases. When the area fraction of the cracks surpasses a critical value, the particulate film ruptures, resulting in the bursting of the oil droplet. Further, the crack area fraction, a critical areal expansion for the crack nucleation, the evolution of the crack area, and the number with the areal expansion are quantified. In addition, the bursting behavior of a droplet in the presence of the nearest neighbor is also discussed in detail.