Nanobubble nucleation dynamics in reacting microdroplets: Insights from confocal laser scanning microscopy and molecular dynamics simulations

Gas-evolving interfacial reactions in microdroplets underpin processes in catalysis, energy conversion, and microreactor technologies, yet the principles of nanobubble nucleation remain unclear. Here, we integrate confocal laser scanning microscopy with coarse-grained molecular dynamics simulations to elucidate hydrogen nanobubble formation during base-catalyzed reactions of liquid organic hydrogen carrier (LOHC) droplets with aqueous NaOH. We reveal a competition-controlled nucleation mechanism governed by gas production rate, asymmetric solubility in droplet and surrounding phases, and water-gas interfacial tension. Nucleation occurs only when local gas concentrations exceed a critical threshold that is largely independent of production rate but strongly influenced by gas solubility in two phases. High production rates shorten induction times and shift nucleation toward the LOHC-water boundary, whereas increased solubility in LOHC or water suppresses nucleation, raising the critical threshold or extracting gas from the droplet. Reduced interfacial tension lowers the nucleation barrier, accelerates onset, and favors interfacial nucleation. These findings establish principles for controlling gas evolution in reactive emulsions, offering design guidelines for interfacial microreactors and nanobubble-enabled catalytic systems.