Anisotropic Spreading of Bubbles on Superaerophilic Straight Trajectories beneath a Slide in Water

Abstract

Although the bubble contacting a uniformly superaerophilic surface has caused concern due to its application potential in various engineering equipment, such as mineral flotation, very little is known about the mechanism of how the bubble spreads on a surface with anisotropic superaerophilicity. To unveil this mystery, we experimentally studied the anisotropic behavior of a bubble (2 mm in diameter) spreading on the superaerophilic straight trajectories (SALTs) of different widths (0.5 mm-5 mm) in water using a high-speed shadowgraphy system. The 1-3 bounces mostly happened as the bubble approached the SALTs before its spreading. It is first observed that the bubble would be split into two highly symmetrical sub-bubbles with similar migration velocity in opposite directions during the anisotropic spreading. Two essential mechanisms are found to be responsible for the anisotropic spreading on the narrow SALTs (W ≤ 2 mm with two subregimes) and the wide SALTs (W ≥ 3 mm with four subregimes). Considering the combined effect of the surface tension effect of SALT and Laplace pressure, a novel model has been developed to predict the contact size r(t) as a function of time. The nice agreement between this model and our experiments reconfirms that the surface tension effect and Laplace pressure prevail over the hydrostatic pressure.

Spontaneous Rising of a Whirling-Swimmer Driven by a Bubble

“…It can be seen that the superhydrophobic coating has a multilayer packing microstructure with the unique ZnO tetrapod. Benefiting from the microstructure morphology, this superhydrophobic coating immersed in water would be covered by a thin plastron of air, , and thus, the bubble can adhere to this attachment area.…”

“…We noticed that the superhydrophobic surface has been widely used in underwater bubble manipulation, and the controlled effect is very attractive. It has been evidenced that the superhydrophobic surface will form a thin air layer (∼μm) on the wall surface underwater and then causes the superaerophilicity of the superhydrophobic surface. − Using the Laplace pressure difference as the driving force, two superhydrophobic tracks were used to manipulate two bubbles’ directional transport and coalescence . Similarly, Song et al designed a serial-wedge-shaped superhydrophobic track to achieve long-distance bubble transportation.…”

Nature-Inspired Superwettability Achieved by Femtosecond Lasers

“…Therefore, the lotus leaves show underwater superaerophilicity. Inspired by lotus leaves, underwater superaerophilicity can be easily obtained by producing micro/nanostructures on a hydrophobic (lowsurface-energy) substrate [93,[196][197][198][199]. The materials with underwater superaerophilicity have a remarkable ability to absorb and capture gas bubbles underwater.…”

Emerging Separation Applications of Surface Superwettability

“…Inspired by lotus leaves, underwater superaerophilicity can be easily obtained by producing micro/nanostructures on a hydrophobic (low-surface-energy) substrate [329][330][331][332][333][334][335][336][337][338].…”