Tunable Persistent Random Walk in Swimming Droplets

Straight-to-Curvilinear Motion Transition of a Swimming Droplet Caused by the Susceptibility to Fluctuations

“…The fastest relaxation time attained ∼1.4 s [Fig. 3(b)], and thus τ min ¼ 1.4 s was a suitable lag time to identify the degree of curved motion as arccos Cðt; τ min Þ. Qualitatively similar behavior has been observed in other experimental systems [22,23]. The oscillatory motion of the large droplets is possibly related to the chaotic motion shown in the previous study [32].…”

“…As a simpler case, spontaneous symmetry breaking of the motion of a swimming droplet in a two-dimensional (2D) system was investigated experimentally [29,30] and theoretically [31], which identified the straight-to-curvilinear motion transition. Recent experimental studies reported that an increase of the external surfactant concentration or the viscosity of the swimming medium causes the curvilinear motion of a swimming spherical droplet [22,23]. In addition, the previous studies showed the existence of a relation between the emergence of the complex motion and the onset of higher hydrodynamic modes [23,32].…”

“…Additionally, swimming droplets are still significant as models of the single and collective motion of living organisms. For example, various "living" motions are observed even in individual droplets [10,[20][21][22][23][24]. However, the emergence of motion diversity is not clearly understood.…”

Alignment and scattering of colliding active droplets

“…19,20 Like phoretic colloids, they drift down an existing gradient of chemical solute (e.g., away from other droplets) and are therefore also antichemotactic. 19,20 In addition to their self-propulsion, active droplets may deform spontaneously, 21,22 exhibit chaotic behaviour [23][24][25] and swim along curly trajectories. 26,27 Active droplets interact with and respond to ambient hydrodynamic flows or chemical gradients, generated by an external forcing, confinement or other active droplets.…”

Chemical Design of Self-Propelled Janus Droplets

“…However, when the number density of droplets was increased such that droplets were forced to swim through regions of solution recently occupied by another droplet, a slowdown in speed accompanied by a slight reorientation in direction often occurred (Figure 6a,b, Video S6). This slowdown is caused by the "exhaust trail" 37 of solubilized oil in micelles left behind as the droplets swim. As the chemical trail ages and oil-filled micelles diffuse, intersecting droplets experienced a smaller drop in speed as they crossed through the trail region (Figure 6b,c).…”