Real-Time Visualization of Interfacial Electric Field Dynamics in Microdroplets.

Real-time observation of electric field dynamics at microdroplet air-water interfaces is critical for understanding and controlling interfacial reactivity. However, existing methods primarily measure steady-state fields or lack the temporal resolution needed to capture rapid interfacial fluctuations. Here, we introduce a fluorescence kinetic imaging technique employing a field-sensitive probe to quantitatively visualize interfacial electric fields during microdroplet coalescence. By calibrating the first-order fluorescence decay of the probe with applied field strength, we map the spatiotemporal evolution of electric fields as droplets fuse and deform. Our results reveal that interfacial electric fields are strongly correlated with droplet morphology, rapidly disappearing upon significant boundary disruption. Additionally, we demonstrate that these electric fields can be externally modulated through molecular additives such as ethanol, which disrupts interfacial ordering. This work establishes a broadly applicable approach for probing interfacial phenomena and offers fundamental insights critical for advancing microdroplet-based technologies in catalysis, and advanced materials.