Herein, we present the first direct observation and quantification of a water-in-oil (w/o) emulsion, its destabilization, and the effect of additives on such processes. This is achieved via liquid phase transmission electron microscopy (LPTEM), which encapsulates a small volume of emulsion against vacuum in its liquid state to allow observation of its initial morphology and its evolution over time, at unprecedented spatiotemporal resolution. Emulsions of this class are useful for delivering payloads of materials insoluble in their delivery medium and are currently used across food science, pharmaceuticals, and environmental applications, but are inherently limited by their thermodynamic tendency to demulsify, eventually leading to bulk phase separation. This occurs via several degradation mechanisms, which are understood individually, but not collectively. These mechanisms (e.g., Ostwald ripening or coalescence) are nearly impossible to differentiate via traditional ensemble methods (e.g., light scattering), which obscure mechanistic nuances. This is exacerbated by the incomplete models of degradation pathways, which lead to inaccurate or biased extrapolations from population data. LPTEM as a characterization technique has the potential to augment understanding of emulsion behavior and improve performance and formulations, as we can observe these processes together for the first time. Employing image analysis tools allows the quantification of rates of demulsification, as well as the visualization of intermediate structures. These observations may inform fundamental models of emulsion behavior and, potentially leading to improved stability via formulation optimization. We have also been able to demonstrate shifts in degradation modes via established strategies (e.g., adding cosurfactants or salts), which hold true for in situ observations as well. We are also able to observe emulsion formation by flowing the dispersed phase into a liquid cell of oil and surfactant. Additionally, we explore the uses of this technique for characterization of emulsion formation and emulsion polymerizations.

Investigating emulsion morphology, dynamics, and formation via liquid phase transmission electron microscopy

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