No Microdroplets? No Problem. Soap Films Amplify the Interface and Produce Hydrogen Peroxide

Recently, several groups have reported remarkable observations concerning the acceleration or promotion of nonequilibrium reactions in aqueous microdroplets. Such observations often implicate the reactivity of the microdroplet interface or the energy used for the formation (i.e., by nebulization, sonication, or electrospray) of these systems with high surface-area-to-volume ratios.. While the input of energy is important for reactions, such as hydrogen peroxide formation, the spatial distribution of that energy, particularly at interfaces, may strongly influence reaction pathways and yields. Moreover, nebulized microdroplets are inherently dynamic and are, therefore, challenging to study systematically. Thus, investigating less dynamic and energetic means of increasing SA:V ratios could provide the community with a platform to explore the intricate mechanisms at play in these systems. Here, we investigated two-dimensional soap thin films, formed by using a commercial soap bubble wand, as a low-cost, low-energy model system to enhance the SA:V ratio. In this study, we evaluate the thin film's ability to promote hydrogen peroxide formation. We demonstrate that the formation of soap films promotes the generation of H₂O₂. Quantitative ultraviolet-visible spectroscopy assays show the concentration of hydrogen peroxide in a soap film on a commercial bubble wand reaches 1.67 ± 0.16 mM. We confirmed hydrogen peroxide formation by commercial test-strips and ¹H NMR. This soap film experiment arguably represents the least-energy-intensive method to enhance SA:V ratio and produce hydrogen peroxide at complex phase boundaries to-date. Our findings establish soap film reactivity as an open avenue of inquiry for phase boundary curious chemistry.