Hypothesis: Monodisperse nanodroplet generation in quenched hydrothermal solution (MAGIQ) is a newly developed bottom-up process for preparing nanoemulsions. In this process, homogeneous solutions of oil in supercritical water are quenched by adding cold water containing a surfactant to induce rapid phase-separation, during which oil molecules self-assemble to form nano-sized oil droplets. The droplet size in MAGIQ is known to be influenced by the interplay of the phase-separation dynamics, coalescence kinetics of the droplets, and adsorption kinetics of the surfactant on the droplet surface; however, the primary stages of the droplet formation are still elusive.
Experiments: Octane‑in‑water nanoemulsions containing 0.5, 1, and 3 vol% octane were prepared by the MAGIQ method. Their ripening was studied by dynamic light scattering, and the phase diagram was established.
Findings: The nanoemulsions containing 0.5 and 1 vol% octane transformed to thermodynamically stable microemulsions containing swollen micelles, whereas the nanoemulsion containing 3 vol% octane underwent Ostwald ripening. The initial formation of the nano-sized droplets in the former was ascribed to a unique mechanism of droplet formation in MAGIQ-the droplets are first formed by the phase separation of homogeneous binary solutions of oil in supercritical water and then stabilized upon surfactant adsorption.
Keywords: Metastable droplets; Monodisperse nanodroplet generation in quenched hydrothermal solution; Nanoemulsion; Octane–water binary mixture; Phase transition; Self-assembly; Supercritical water.
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