Phototaxis Flight of Microdroplets in a Laser

Phototaxis phenomenon is fundamental and critical for optical manipulation of micro-objects. Here, we report the size-dependent negative or positive phototaxis behaviors for microdroplets containing interfacial energy absorber flying in a laser. The critical diameters for such negative-to-positive turnover are studied through both experiments and simulation with different liquids and absorbers, which establishes the mechanism and reveals the role of both the liquid and the absorber inside the microdroplets. This study offers new insight for the manipulation of the phototaxis behavior of micro-objects, showing potential applications in optical trapping and transporting systems that involve light-microdroplet interactions.