Ultrasound-based formation of nano-Pickering emulsions investigated via in-situ SAXS

Sonication is one of the most commonly used methods to synthesize Pickering emulsions. Yet, the process of emulsion sonication is rarely characterized in detail and acoustic conditions are largely determined by experimenter's personal experience. In this study, the role of sonication in the formation of Pickering emulsions from amphiphilic gold nanoparticles was investigated using a new sample environment combining ultrasound delivery with ultra-small-angle X-ray scattering (USAXS) measurements. The detection of acoustic cavitation and the simultaneous analysis of structural data via USAXS demonstrated direct correlation between Pickering emulsion formation and cavitation events. There was no evidence of spontaneous adsorption of particles onto the oil-water interface without ultrasound, which suggests the presence of a stabilizing force. Acoustically detected cavitation events could originate in the bulk solvent and/or inside the emulsion droplets. These events helped overcome energy barriers to induce particle adsorption.