Presentation Information
[9a-N221-2]Spontaneous Rotation Mechanism of Droplets Induced by Laser Photothermal Conversion
〇(D)Shinya Hakuta1, Masayuki Naya1,2, Jintaro Shiina1, Toshiharu Saiki1 (1.Keio Univ., 2.Naya lab.)
Keywords:
photothermal Conversion,optical manipulation,self-propelled motion
This study elucidates the spontaneous rotation mechanism of microdroplets induced by laser photothermal conversion in a confined ethanol/PEG200 mixture. Upon localized laser heating, microdroplets are generated and initiate spontaneous rotation for over ten minutes at ~0.5 mW laser power. Optical microscopy reveals a PEG-rich “tail” formed during rotation, suggesting two driving forces: (1) photothermally induced Marangoni attraction toward the irradiation site and (2) surface-tension pull from the PEG tail. We construct a nonlinear dynamic model decomposing these two forces plus friction, which mathematically reduces to a Stuart–Landau-type limit-cycle oscillator. Numerical simulations reproduce the observed decrease in orbital radius and period with increasing laser power, in quantitative agreement with experiments. The hybrid experimental–numerical approach offers a quantitative framework for active-matter droplet control and potential applications in optothermal micro-robotics.