Two-Photon 3D Printing of Hydrophobic Membranes to Control Gas-Liquid-Solid Interfaces

Controlling the degree of wetting and maintaining stable gas-liquid-solid interfaces are critical for a range of applications where species exchange between the liquid phase and the gas phase limits the rate and efficiency of desired chemical or electrochemical reactions. Previous works on hydrophobic surfaces explored materials chemistries as well as geometric motifs to increase the energy barrier between the meta-stable Cassie-Baxter state, where the liquid stays on top of the structured surface with gas pockets (i.e., plastrons) trapped underneath it, and the fully wetted Wenzel state. This concept was originally inspired by biological surfaces such as lotus leaves and duck feathers with self-cleaning and water-repelling capabilities. The next level of development is to design and engineer hydrophobic membranes that can prevent wetting by certain liquids while allowing fast permeation of gaseous species. Such functionality is important for applications like vapor-fed electrochemical CO₂ reduction reactors, ECMO oxygenator membranes, and water-resistant yet breathable fabrics. In this work, we use two-photon lithography to 3D print micro-architected membranes made out of fluoropolymers to enable accurate control of stable gas-liquid-solid interfaces. The high printing resolution allows for systematic integration of microscale pores (1-10µm) with high liquid breakthrough pressure and large gas-liquid interface fraction. Optimized 3D architecture can fine tune the location of gas-liquid interfaces and maximize gas permeance across the thickness of the membrane. We demonstrate that 3D-printed, micro-architected hydrophobic membranes can function as idealized gas diffusion electrodes for electrochemical CO₂ reduction and efficient gas exchange membranes for microfluidic artificial lungs.