Fig. 7: Initiation of the Marangoni transport system and rotation of the filament.

a Marangoni convection induced by the deposition of a tiny amount of DEX-MB-CaCl₂ (<0.05 μL) on the surface of a PEG-SDBS solution (2.5 mM) containing tracer particles (diameter 22 μm) in a glass cuvette. The green lines are the trajectories of the PS particles during 5 s. The pink dots indicate the current positions of the PS particles. b Diffusion of MB and CaCl₂ from a DEX-MB-CaCl₂ droplet (1 μL) that was carefully deposited at the bottom of the PEG-SDBS (2.5 mM) bulk solution. c Schematic of the surface tension difference while the spiral pattern is rotating. d Time-varying average frequency f_r(t) determined from the spiral patterns produced by the addition of a droplet of DEX-MB-CaCl₂ (50 mM) to a cell (diameter 15.8 mm) filled with PEG-SDBS (50 mM) solution containing 0, 0.05, and 0.2 mM of CaCl₂, respectively.