Direct Observation of Emulsion Morphology, Dynamics, and Demulsification

Abstract

Herein, we present the direct observation and quantification of a water-in-oil (w/o) emulsion, its destabilization, and the effect of additives on such processes at the nanoscale. This is achieved via liquid phase transmission electron microscopy (LPTEM), wherein a small volume of emulsion is encapsulated against vacuum in its liquid state to allow observation of its initial morphology and its evolution over time at excellent spatial and temporal resolution. Emulsions of this class are useful for delivering payloads of materials insoluble in their delivery medium and are currently widely used across food science, pharmaceuticals, and environmental applications. However, their utility is inherently limited by their thermodynamic tendency to demulsify, eventually leading to bulk phase separation. This occurs via several degradation mechanisms, operating at times collectively, and which are difficult to differentiate via traditional ensemble methods (e.g., light scattering), obscuring mechanistic nuances. LPTEM as a characterization technique has the potential to augment our understanding of emulsion behavior and improve performance and formulations. In this work, we also emphasize the importance of the included videographic Supporting Information data in demonstrating the behavior of the studied materials.

The Growth Dynamics of Organic–Inorganic Metal Halide Perovskite Films

“…When the supersaturation of the precursor solution is high, the growth rate is proportional to the grain size, which results in relatively slow growth of small nanocrystals and faster growth of larger crystals. As the precursor concentration drops, many smaller perovskite nanocrystals dissolve back into the solution (Figure A: t – t 0 = 798 – 895 s), while the growth rate of larger nanocrystals increases (Figure B), which is a sign of the Ostwald ripening process. − It should be noted that we also observed few larger grains dissolving and few smaller grains surviving (Video S3), so the grain stability does not only depend on its size but likely also on the local variations in the precursor concentration. When compared to the case without urea, we see that perovskite nanocrystals dissolve more easily in a urea-containing precursor solution.…”

Caught in Action: Visualizing Dynamic Nanostructures Within Supramolecular Systems Chemistry

“…Furthermore, for the first time, the radial growth profile of diphenylalanine nanotubes was observed, where monomers attach perpendicular to the tubular axis to increase the width of the tube (Figure 4j–k). The same group also used LP‐TEM to probe the emulsion formation of sodium salt of dioctyl sulfosuccinate and its demulsification in real‐time [50] . Most emulsions are studied in the bulk using light scattering methods which does not provide the mechanism of transformation over time.…”

Caught in Action: Visualizing Dynamic Nanostructures Within Supramolecular Systems Chemistry

“…Copyright 2021 ACS; (f)–(k) reference [49]. Copyright 2021 ACS; (l)–(m) reference [50]. Copyright 2022 ACS.…”

“…The same group also used LP-TEM to probe the emulsion formation of sodium salt of dioctyl sulfosuccinate and its demulsification in real-time. [50] Most emulsions are studied in the bulk using light scattering methods which does not provide the mechanism of transformation over time. The reported investigation on emulsion using LP-TEM was able to screen the various pathways involved in emulsion formation like coalescence, Ostwald ripening and flocculation for emulsion evolution towards phase separation (Figure 4l, m).…”