Ultraviolet-Driven Janus Foams with Wetting Gradients: Unidirectional Penetration Control for Underwater Bubbles

Abstract

Understanding the behavior of underwater bubbles and enabling their effective manipulation is important for bubble capture, collection, and transport. Here, to discuss the underwater permeation behavior of bubbles and critical influencing parameters in this process, the copper foams with tunable wettability were fabricated by utilizing the light-stimulated wettability response of TiO 2 . The Janus copper foams had different wettability gradients from superhydrophobic/hydrophobic to superhydrophobic/hydrophilic after UV irradiation at different times, and the bubbles on the surfaces showed distinctly diverse penetration behaviors. In particular, the constructed superhydrophobic/hydrophilic surfaces showed more difficult to achieve bubble penetration than the fully superhydrophobic, superhydrophobic/hydrophobic surface. It was found that the wetting states of the foams exposed to different irradiation times underwater plays a crucial role in the bubble penetration behavior. In other words, the difficulty of bubble penetration depends on the difficulty of bubble transition from gas− liquid contact to gas−solid contact. This facile and low-cost fabrication approach for Janus foams provided a valuable approach to understand the penetration behaviors of underwater bubbles, which is significant for expanding potential applications in bubble capture, bubble transport, and control of unstable gas reactions in underwater conditions.

An Experiment and Molecular Dynamics Simulation of Synergistic Foaming between a Surfactant and CO2 and the Structure–Activity Effect

“…Once the foam is generated, it undergoes uneven liquid film flow due to the combined effects of gravity and pressure gradients. Additionally, the gas within the foam continues to diffuse and permeate through the foam film, driven by the pressure disparities between its two sides [28]. The gas diffusion through the liquid film and the liquid film drainage only play an obvious role in the initial stage of the formation of the foam system.…”

“…The HLB values for AOS [32], Furthermore, no consistent relationship was observed between the hydrophilic-lipophilic balance (HLB) values and solubility parameters. The HLB values for AOS [32], SDBS [33], AES [34], SLES [35], CHSB [28], CAB [36], 6501 [37], and APG0814 were 15.4, 10.6, 14, 14, 8.7, 13.48, 14, and 12.45, respectively.…”

Spontaneous Directional Transportation Surface of Water Droplet and Gas Bubble: A Review

“…It also could be used for the elimination and collection of gas bubbles in containers. Dai et al [112] used UV radiation technology to modulate the wettability of the TiO 2 -sprayed copper foam surface. They found that the difficulty of gas bubble penetration depended on the difficulty of their transition from gas-liquid contact to gas-solid contact.…”

Underwater Bubble Manipulation on Surfaces with Patterned Regions with Infused Lubricants

“…12 In 2022, Guo et al successfully prepared Janus foam copper with a wettability gradient, which can realize rapid switching of wettability under UV illumination and flexible control of bubble penetration. 13 However, the underwater bubbles are manipulated in a high-pressure, high-humidity environment, which makes the superhydrophobic surface susceptible to failure after prolonged immersion. This, in turn, weakens the surface's ability to adhere to and spread on the bubbles.…”

“…In 2021, Xiao et al successfully prepared a two-dimensional superaerophilic surface embedded with asymmetric aerophilic barriers, enabling the unidirectional long-range transport of gas bubbles . In 2022, Guo et al successfully prepared Janus foam copper with a wettability gradient, which can realize rapid switching of wettability under UV illumination and flexible control of bubble penetration . However, the underwater bubbles are manipulated in a high-pressure, high-humidity environment, which makes the superhydrophobic surface susceptible to failure after prolonged immersion.…”