title: Extraordinarily Rapid Rise of Tiny Bubbles Sliding beneath Superhydrophobic Surfaces.
abstract: Tiny bubbles readily stick onto substrates owing to contact angle hysteresis (CAH). Nevertheless, they can slide slowly on a tilted surface with ultralow CAH because capillarity is overcome by buoyancy. It is surprising to observe experimentally that bubbles of 3-15 μL (diameter 1.79-3.06 mm) slide beneath a tilted superhydrophobic surface at a vertical ascent rate faster than that of freely rising ones of high Reynold numbers ≈O(102). As the tilting angle increases, the drag coefficient remains essentially the same as that of a freely rising bubble, but the frontal area of the flat bubble rises monotonically. Nonetheless, the frontal area of the sliding bubble always stays much smaller than that of a freely rising bubble. Consequently, the small drag force associated with the sliding bubbles is attributed to their substantially small frontal areas on superhydrophobic surfaces.
authors.forename: Cyuan-Jhang
authors.initials: CJ
authors.lastname: Wu
authors.affiliation: Department of Chemical Engineering, National Taiwan University , Taipei 106, Taiwan.
authors.forename: Cheng-Chung
authors.initials: CC
authors.lastname: Chang
authors.affiliation: Department of Chemical Engineering, National Taiwan University , Taipei 106, Taiwan.
authors.forename: Yu-Jane
authors.initials: YJ
authors.lastname: Sheng
authors.forename: Heng-Kwong
authors.identifier: 0000-0001-6415-8657
authors.initials: HK
authors.lastname: Tsao