Figure 2: Spontaneous dynamic behaviour of PFOB spread on water.

(a) PFOB is pipetted onto a water surface. (b) Immediately after contact with water, it spreads to form a thin film. On the basis of the injection volume (8 μl) and the surface area of water (∼65 cm²), the thickness of the film can be estimated to be 1 μm. (c,d) As the PFOB gradually evaporates, the system exhibits characteristic pearling phenomena consisting of four successive non-equilibrium events; event I: a water hole is generated through the evaporation of PFOB molecules and the dewetting transition; event II: fluorocarbon humps are formed on the rim of the water holes, which causes circular pearling of the droplet array; event III: appearance of a linear pearling (1D array), where droplets are generated periodically; event IV: (d) a regular hexagonal 2D structure is formed over the entire water surface by rhythmical shrinking and expanding motion, and remains for a relatively long time as a stable pattern. Finally, the arranged droplets disappear within 20 s due to evaporation.