Janus Membranes with Asymmetric Wettability for Fine Bubble Aeration

Abstract

aeration. The membrane is consisted with a hydrophilic/superaerophobic coating on a hydrophobic porous support, which shows cooperative water and gas penetration. [19][20][21][22][23][24][25] The superaerophobic side allows rapid bubble detachment and reduced bubble size, while the hydrophobic side prevents water from permeating through the membrane pores and traps gas into the pores to lower the intrusion pressure. As a result, we have achieved greatly improved gas/liquid mass transfer, as exemplifi ed with both O 2 involved dopamine (DA) oxypolymerization and CO 2 involved biocatalytic hydration processes.As we mentioned above, superaerophobicity can be achieved by adjusting the surface wettability and hierarchical structures. Considering the porous nature of typical polypropylene membrane, we hydrophilized its surface to improve aerophobicity. To this end, we conducted single-sided polydopamine/polyethyleneimine (PDA/PEI) codeposition for asymmetric surface modifi cation. [26][27][28] The ethanol prewetted polypropylene membrane was fl oated on a DA/PEI solution for 4 h as illustrated in Figure 1 a. Then the Janus membrane was obtained and the immersed side turned brown after deposition (Figures S1 and S2, Supporting Information). The pore size shows no obvious change after modifi cation ( Figure S3, Supporting Information). The PDA/PEI-modifi ed side is signifi cantly hydrophilic and the water drops infi ltrate into the membrane pores immediately, while the other side remains hydrophobic with an initial water contact angle of about 110° (Figure 1 b). However, the water drops gradually permeate through the membrane pores with the decrease of contact angle and drop conjugate diameter (CD), which is caused by the directional transport of water within a Janus membrane. [ 19 ] We also investigated the submerged gas wetting behaviors on the membrane surfaces. The unmodifi ed surface is moderate aerophilic with a GCA around 80°, arising from its hydrophobicity and air trapped in the membrane pores ( Figure 2 a), while the PDA/PEI-modifi ed side is superaerophobic and repels to air bubbles (Figure 2 b). The gas adhesion work was calculated by detecting the GCA on a fl at polypropylene fi lm, which decreases from 61.3 to 6.29 mJ m −2 after hydrophilic modifi cation. The porous structure will further reduce the apparent gas adhesion work according to the Cassie-Baxter model. [ 29 ] The decrease of triple phase contact line (TPCL) leads to low air adhesion on the membrane surface during the bubbling process.The bubble formation process was recorded by a high-speed camera to investigate the effects of surface wettability on bubbling behavior. Figure 2 c shows that a hemispherical bubble grows on the gas/solid interface when bubbling through the nascent membrane. It detaches from the surface until the gas/ solid CD reaches 4 mm, leaving a thin gas fi lm on the membrane surface. In contrast, a spherical bubble is observed in the Bubble aeration has been widely applied in many processes for energy production, environmental ...

Superwettability of Gas Bubbles and Its Application: From Bioinspiration to Advanced Materials

“…[66,67] A superhydrophobic/hydrophilic cooperative Janus mesh is fabricated via a facile singleface coating process under the assistance of liquid surface tension (Figure 7a-c). [66] In aqueous media, a Janus membrane Figure 5.…”

“…[67] Owing to the low adhesive force applied to gas bubbles, the superaerophobic side allowed the rapid detachment of gas bubbles and greatly reduced bubble release size. The hydrophobic side exhibits aerophilicity for gas bubbles and hydrophobicity for water at the same time.…”

Novel Water Harvesting Fibrous Membranes with Directional Water Transport Capability

“…[3][4][5][6] These excellent water harvesting creatures elucidate the critical role of wettability irregularity and hierarchical structure gradient in guiding water transport. [23][24][25][26][27][28][29][30] Our previous works have reported the preparation of hydrophobic-to-hydrophilic gradient fabrics that can guide directional water-transport from the hydrophobic to the hydrophilic side. [19][20][21][22] However, most of the water harvesters developed so far are based on either a 2D surface or a 1D filament.…”

Reversible switch between underwater superaerophilicity and superaerophobicity on the superhydrophobic nanowire-haired mesh for controlling underwater bubble wettability

“…15 Although some underwater superaerophobic and superaerophilic surfaces have been successfully fabricated, the related research is still at an initial stage. 1,2,[16][17][18] Those artificial materials usually have single and fixed super-wettability to underwater bubbles, either underwater superaerophobicity or underwater superaerophilicity. To obtain multifunctional applications, a smart surface that can reversibly switch between underwater superaerophobicity and superaerophilicity by a simple way is especially significant but has not been reported until now.…”