Spontaneous change in trajectory patterns of a self-propelled oil droplet at the air-surfactant solution interface

Abstract

Trajectory-pattern formation of a self-propelled oil droplet floating on the surface of a surfactant solution in a circular dish is studied both experimentally and by simulation. The Marangoni effect induced by the dissolution of oil in the solution drives the droplet's motion. The trajectories spontaneously organize into several patterns including circular, knot-forming, back-and-forth, and irregular ones. They are either global patterns, whose center corresponds to the dish center, or other local patterns. Our simple model consisting of three forces, the driving force, the viscous resistance, and the repulsion from the boundary, successfully reproduces the global trajectory patterns including the power spectrum of the droplet speed.

Motion of a Spot in a Reaction Diffusion System under the Influence of Chemotaxis

“…Although symmetric droplets cannot move in the absence of external force, the Marangoni effect can cause motion in the presence of an inhomogeneous chemical substance outside the droplet or a temperature gradient along the surface [4][5][6]. Numerical simulations and theoretical results support this mechanism and the existence of straight, circular, and complicated motions of droplets [7,8], and experimental results qualitatively agree with the numerical results [9][10][11][12]. Droplet motion has also been the subject of a review article [13,14].…”

Relationship between the size of a camphor-driven rotor and its angular velocity

“…The same idea applies for rotational motion, as well. The rotational motion is relevant as it can occur even in a confined geometry [5][6][7]. In order to realize the rotational motion, we also have two strategies, i.e., asymmetry embedded into the system and spontaneous symmetry breaking.…”

Periodic collective behaviors of organic solvent droplets on the surface of aqueous surfactant solutions

“…We found a complex collective mode of motion of droplets, which consist of only a few chemically simple molecules. These droplets are driven by inhomogeneous surface tension field around them, which is created by the dissolution of ES from the droplets (Tanaka et al, 2015). They interact with each other through the surface tension field, as well as First, the droplets do not easily merge together, even if they seem to touch with each other.…”

“…Recently we found even more complex behaviors in a system of organic-solvent droplets floating on aqueous solution (Tanaka et al, 2015(Tanaka et al, , 2017Čejková et al, 2019). There, dissolution of organic solvent from droplets decreases the surface tension of aqueous surface, which propels the droplets.…”