Deep-sea-inspired bottom-up nanoemulsification of alkyl esters in water

Monodisperse nanodroplet generation in quenched hydrothermal solution (MAGIQ) represents a bottom-up strategy for nanoemulsion preparation. In this process, a homogeneous alkane solution in supercritical water is rapidly quenched by mixing with cold, surfactant-containing water, triggering phase separation and spontaneous self-assembly of oil molecules into nanodroplets. Inspired by the dynamic thermal environments of deep-sea hydrothermal vents, this method ensures only transient exposure of alkanes to elevated temperatures, thereby minimizing thermal degradation. However, its applicability to alkyl esters, an important class of oils widely used in practical formulations but prone to hydrolysis under extreme aqueous conditions, remains unexplored. Here, we applied the MAGIQ process to prepare nanoemulsions of two alkyl esters commonly used in cosmetic formulations-hexyl dodecanoate and 2-ethylhexyl hexadecanoate-in water. Molecular dynamics simulations confirmed the dissolution of these esters in sub- and supercritical water. Oil-in-water nanoemulsions were successfully generated through the MAGIQ process, with spontaneous nanodroplet formation upon quenching. Remarkably, hydrolysis of the alkyl esters was negligible, likely due to the brief high-temperature exposure and suppressed water ionization near the critical point. These findings significantly extend the scope of emulsifiable oils and demonstrate the versatility of the MAGIQ process beyond alkanes.