Oleic Acid-Mediated Double Emulsification Enables Enhanced Aqueous Stability and Localized Photothermal Heating of Liquid Metal Droplets.

Gallium-based liquid metals (LMs) have emerged as promising photothermal agents owing to their broadband optical absorption, high photothermal conversion capability, and intrinsic fluidity. However, their practical implementation in aqueous and biological environments remains severely limited by water-induced oxidation and hydrolysis, which progressively deteriorate their structural and photothermal stability. Here, we present a facile and potentially scalable double-emulsion strategy that physically isolates LM nanodroplets from water without requiring complex surface modification. By dispersing eutectic gallium-indium (EGaIn) nanodroplets within an oleic acid (OA) intermediate phase and subsequently emulsifying the system in water, a yolk-shell-type LM-in-OA-in-water (LM/OA/W) architecture is spontaneously formed through wettability-driven confinement. The OA phase serves as both a barrier against water transport and a thermally insulating microenvironment. Consequently, the double-emulsified LM exhibits improved aqueous stability and amplified photothermal performance compared with conventional LM/water dispersions, while retaining its morphology and functionality during prolonged aqueous storage and repeated near-infrared irradiation. Furthermore, the double-emulsion platform demonstrates low acute toxicity, effective photothermal suppression of three-dimensional tumor spheroids, and facile incorporation of additional functional components. This work establishes wettability-driven double emulsification as a simple yet versatile strategy for stabilizing and multifunctionalizing LM-based photothermal systems.