Figure 4. Continuous self-transport of the drops on the surface of spine.

(a) Continuous self-transport of drops on spine. The subsequent drop 2 moved fast in the time from ~156 s to ~157 s after the initial drop 1 passed over the surface of spine in time of ~1–152 s. The insets show the process of subsequent drop 2 that moved fast to the bottom of the spine in ~156.14–156.20 s. (b) Moving distances versus time of the initial drop (drop 1) and subsequent drop (drop 2). The average velocity of drop 1 can be estimated with β₁, that of drop 2 is β₂ (β₂ > β₁), indicating drop 2 moved much fast than drop 1.