Figure 1.
The evolution of self-driven droplets.
The development process from immobile droplet to self-driven droplet. SEM images in a 45-degree viewpoint are as follows: (a) a “baby” stage droplet with circular contact line; (b) a “child” stage droplet with rounded-rectangular shape contact line, is learning to walk; (c) is a “teenage” droplet with hexagonal-face shape contact line, is in the beginning stage of walking; and (d) is an “adult” droplet with a hexagonal-face-shape contact line, is in the early stage of stick-slip motion.
Figure 2.
The morphology of running Ga droplets.
The typical footprints of Ga droplets motion are: (a) a SEM image of running droplets in microscale; (b) a SEM image of the detailed footprints left behind by the leading droplet in nanoscale; (c) AFM images of the footprint from droplet motion: (c1) the simple topographical AFM mapping; (c2) AFM phase image highlighting the stepping nanostructures of footprints; and (c3) AFM 3D images revealing the depth of the footprints with the central dashed-line corresponding to the AFM line-scanning profile on the right-hand side graph. The multiple dashed-lines on the scanning-line graph indicate the footprint are featured in angles α and β (α = 1.6° and β = 6.4° after ratio normalization). Finally, (d) is the AFM 3D image of a moving droplet, with the central dashed-line corresponding to the AFM line-scanning profile on the right side.
Figure 3.
Collision between two running droplets.
The two droplets are coincident with each other: (a) Before colliding, in top view of SEM, both the shape of droplets A and B are confined in their moving trails. (b) After colliding, in the top view, droplet A merges with droplet B. The orange circular shape indicates the original droplet B before colliding resulting in an empty well with a group of small droplets in position A. (c) the top view shows the schematic diagram of the droplet coalescence. The orange circle indicates the droplet before collision; the red dot-dashed circle indicates the coalescent droplet, and the red dash line in position A indicates the roundish well after collision. Both (d1) and (d2) are SEM images which show that the resultant larger droplets from coalescence are moving backward and forward. (e) This shows the AFM 3D image of the coalescent event. The red dash-square area corresponds to the simple topographical AFM mapping (top side) in which the atomic scale layers highlight the atomically flat bottom of the well. The two black dash-lines correspond with the AFM line-scanning profile graphs (right side), outlining the significant depth of the well by comparing them with the trail.
Figure 4.
Freshly exposed surfaces from colliding events.
Images (a), (b), and (c) are SEM images of coincident events in top view. Both (d) and (e) are SEM images of coincident events in a 45-degree viewpoint, where roundish deep wells are clearly visible in the A positions of each. Both (f) and (g) are schematic diagrams of the droplet coalescence. (e) In the top view, the orange circle indicates the droplet before the collision; the red dot-dash circle indicates the coalescent droplet, the red dash line in position A indicates the roundish well after collision. (f) In the cross-section view, the orange ellipse indicates the droplet before colliding; the red dot-dash ellipse indicates the coalescent droplet, and the red dash line in position A indicates the roundish well after collision. The wavelike surface indicates the footprints left behind by the droplets.