High-Throughput Electrospinning System| Springtail-inspiredomniphobicslipperymembranewith nano-concave re-entrantstructures formembrane distillation

 Nature Communications: Springtail-Inspired Omniphobic Lubricated Membrane with Nanoscale Concave Structures for Membrane Distillation Wastewater Treatment

A research team led by Professor Yi Chunhai from Xi'an Jiaotong University, in collaboration with Professor Alicia Kyoungjin An's team from City University of Hong Kong, has developed a superhydrophobic and oleophobic omniphobic membrane featuring springtail-inspired micro-nano concave surface structures. The paper, titled "Springtail-inspired omniphobic slippery membrane with nano-concave re-entrant structures for membrane distillation," was published in Nature Communications. The first author of the paper is Special-Term Researcher Guo Jiaxin from Xi'an Jiaotong University, with the School of Chemical Engineering and Technology at Xi'an Jiaotong University as the primary affiliation.

Figure 1:Graphical abstract: Omniphobic membrane with concave micro-nano surface structures inspired by springtail skin.

With increasingly severe water scarcity issues, developing novel desalination technologies has become crucial. Membrane distillation technology, as a promising method, offers advantages in treating high-salinity wastewater. However, traditional membrane distillation membranes are susceptible to low surface tension contaminants, leading to membrane wetting and decreased salt rejection rates. To overcome this bottleneck, this study was inspired by springtail skin and developed an omniphobic membrane with nano-concave structures using electrospray technology for efficient seawater desalination.

Figure 2:(a-d) Scanning electron microscopy (SEM) images of surface morphology for (a) PS1, (b) PS2, (c) PS3, and (d) PS4 membranes, with higher magnification SEM images shown in insets.(e) Water contact angle (CA) measurements based on surface energy information.(f) Results of abrasion tests and stability evaluations under different pH conditions (see Appendix).(g) Schematic of the fabrication process for biomimetic concave PS bead-coated omniphobic membranes.Error bars represent standard deviations from three independent measurements.

This study employed electrospray technology to prepare polystyrene (PS) nanoparticles with concave structures, which were then coated onto commercial polyvinylidene fluoride (PVDF) membranes. By controlling environmental humidity and applied voltage, the morphology of PS particles was optimized to form concave structures resembling springtail skin. Subsequently, a low-toxicity short-chain perfluoropolyether (PFPE) lubricant was applied through dip-coating to further reduce surface energy and impart omniphobicity to the membrane. The study adopted a plasma activation strategy to introduce hydroxyl functional groups on the substrate membrane surface, which underwent dehydration condensation reactions with carboxyl groups in the lubricant to form a covalent cross-linked network, optimizing the interfacial bonding strength between the coating and substrate membrane.

Figure 3:Schematic diagram of spherical and concave PS bead formation during electrospray process.

The main innovation of this study lies in using electrospray technology to create nano-concave structures and employing low surface energy lubricants to achieve membrane omniphobicity. Compared to traditional wet/dry etching and photolithography techniques, electrospray technology is simpler and more feasible while enabling precise control of nanostructure morphology. The nano-concave structures effectively increase the membrane's surface roughness, while the low surface energy lubricant reduces surface energy. Their synergistic effect gives the membrane excellent omniphobicity, effectively resisting wetting by low surface tension liquids.Experimental data show that the optimized PS4L2 membrane exhibits a water contact angle of 171.1°, oil contact angle of 139.6°, surface energy of 12.39 mN/m, and porosity as high as 87.4%. When treating seawater containing 1.0 mM sodium dodecyl sulfate, the membrane maintained a stable 99.9% salt rejection rate, significantly outperforming conventional membranes and demonstrating excellent membrane distillation performance.

Figure 4:(a) Molecular dynamics (MD) performance analysis of C-PVDF, PS4, and PS4L2 membranes.(b) Optical coherence tomography (OCT) images of membrane surfaces after MD simulation.(c) Schematic illustration of the anti-wetting mechanism of membranes with nano-concave re-entrant structures.(d) Study on the interaction mechanism between nanostructures and feed solution based on fluid flow and particle tracking simulations.

Finally, the omniphobic membrane developed in this study shows great potential in seawater desalination, providing new ideas for addressing water scarcity issues. In the future, we will further optimize membrane performance and explore its applications in other fields to contribute to sustainable development.