[17a-WL2_301-1~11] 3.1 Basic optics and frontier of optics

10:30 AM - 10:45 AM JST(1:30 AM - 1:45 AM UTC)

[17a-WL2_301-6] Spontaneous Rotation Mechanism of Laser-Induced Active Matter Droplets in Micro-Gaps

〇Shinya Hakuta¹, Masayuki Naya¹, Jintaro Shiina¹, Miyu Shimizu¹, Toshiharu Saiki¹ (1.Keio Univ.)

Keywords:

Active matter,Microfluidics,Marangoni Effect

We report a laser-driven active droplet system in a ~3 µm micro-gap. Local laser heating (0.1–1 mW) on-demand writes and erases a flattened droplet in an ethanol/PEG mixture; the droplet follows the beam and exhibits stable spontaneous rotation despite an axisymmetric geometry. The droplet (H ~1 µm, D ~100 µm) has a small Laplace pressure (~35 Pa). A lubrication (Hele–Shaw) estimate shows the lateral vapor-transport pressure scales as ΔP ~ g^-3 and can exceed the Laplace pressure, strongly deforming the interface while avoiding liquid bridging. An opposing wetting film acts as a condensation sink, enabling micro-distillation (evaporation–condensation cycling) that promotes growth with an approximate 1/g dependence in our model. We propose that the competition between growth (~ 1/g) and hydraulic resistance (~ g^-3), coupled with thermal/solutal Marangoni stresses, amplifies fluctuations and triggers spontaneous symmetry breaking that initiates self-sustained rotation.