An Integrated Janus Mesh: Underwater Bubble Antibuoyancy Unidirectional Penetration

Abstract

Gas bubbles are a powerful tool with applications in particle visualization, spacers, actuation pistons, and pressure sensors. Controlling the transportation of bubbles in the liquid phase is a challenge that needs to be solved in many industrial processes, such as in the pipe transportation of fluids, the corrosion of ocean vessels, and the control of foaming processes. There are few existing materials capable of the antibuoyancy unidirectional transportation of bubbles. Here, a Janus superwetting mesh is fabricated by integrating aerophilic (AL) and superaerophobic (SAB) surfaces. The resulting composite mesh achieves underwater bubble antibuoyancy unidirectional penetration. In aqueous solution, bubbles pass through the mesh from the SAB side to the AL side, but are blocked from passing through in the opposite direction. This Janus mesh can be considered to be a bubble diode, so is convenient for use in underwater bubble unidirectional transportation. This work may promote the development of advanced materials for gas bubble directional transportation and separation in aqueous media.

Asymmetric Surface Engineering for Janus Membranes

“…Two‐layer compositing is a common way for the asymmetric fabrication. For example, oppositely wettable metal meshes [ 16–20 ] or porous anodic alumina [ 21 ] membranes are directly integrated into a Janus membrane. Layer‐by‐layer electrospinning is able to establish a two‐layered Janus nanofibrous membrane by sequentially electrospinning hydrophobic nanofibers onto hydrophilic ones and vice versa.…”

“…The asymmetric pore size configuration can also be realized via bonding two membrane layers with different pore sizes. For example, directly integrating two meshes with different pore sizes is a facile way to construct asymmetric pores, [ 17,18,20 ] but the porosity would be reduced to some extent due to the mismatching of pores at the interface. Moreover, electrospinning is able to control the pore size of nanofibrous membranes through changing the concentration of electrospinning liquid or electrospinning parameters such as needle size, electric field intensity, and operation time.…”

“…[ 70 ] Usually, the hydrophilic layer is aerophobic while the hydrophobic one is aerophilic under water. [ 18,83,84 ] The driving force of gas transport relies on the Laplace pressure difference ( P Laplace ) caused by the different states of gas bubbles on each surface of the Janus membranes, and can be calculated by Equation : where γ is the surface tension of water, R 1 and R 2 are the curvature radius of gas bubble on the aerophobic layer and the aerophilic layer, respectively. Note that R 2 has an infinite value when gas bubbles spread on the aerophilic layer and then form a gas film (Figure 8c).…”

Biocompatible Janus Membrane with Double Self‐Healing Ability for Intelligent Anticorrosion

“…[ 3 ] The concept of directional permeability was first introduced in 2010 and has attracted considerable attention in membrane research in recent years. [ 4–16 ] The main idea of directional permeability is to achieve a novel separation performance by having two layers of opposite capabilities. The application of Janus membranes is mainly concentrated in the field of oil–water separation, and they are expected to become a new candidate to replace traditional separation membranes.…”

“…[ 5–7 ] In recent years, Janus membranes have been extensively applied to battery diaphragms, [ 8–10 ] water collection, [ 11–13 ] and ultra‐fine bubbling. [ 14–16 ] Jiang et al [ 2 ] conducted an in‐depth study on the principle of directional permeation in porous Janus membranes and found that when the hydrophobic layer was placed at the top of the membrane, water easily passed through membrane layers; however, when the hydrophilic layer was placed at the top, water only spread over the membrane surface. When Janus membrane is properly designed, the presence of micropores cannot cause the penetration of water.…”