The origin of spontaneous oxidation in a floating oil nanofilm

Nanoscale geometries can profoundly alter chemical reactivity, yet platforms that isolate and control this regime remain limited primarily to microdroplets. Here, we introduce a simple, surfactant-free method to generate a floating oil nanofilm by trapping a gas bubble at the interface between immiscible aqueous and organic phases. This geometry produces a stable, suspended organic film approximately 100 nm thick with a surface-area-to-volume ratio of 10⁷ m^-1, mimicking a droplet with a radius of 300 nm, bounded by closely spaced gas|liquid and liquid|liquid interfaces without a solid substrate. Using electrochemistry combined with finite-element modeling, we quantitatively characterize the nanofilm thickness and show that it enables spontaneous oxidation chemistry that is greatly accelerated compared to bulk systems. Decamethylferrocene undergoes pronounced oxidation within the nanofilm within seconds, in contrast to 10 s of hours required at bulk liquid|liquid interfaces. This behavior is absent under oxygen-free conditions and can be tuned by selective ion transfer across the interface, implicating charge compensation as an important factor in enhanced interfacial chemistry. By accelerating redox processes that are otherwise slow or inaccessible in bulk systems, the floating liquid nanofilm establishes a distinct regime of interfacial reactivity and provides a versatile platform for probing chemical transformations under nanoscale confinement.