Fast Cross-scale Preparation of Water-repellent Hierarchical Surface via Atmospheric air Plasma for Water-in-oil Emulsion Separation

Normally, atmospheric air plasma is usually utilized to hydrophilize the substrate surface. In this paper, a facile and fast method is reported to prepare hierarchical superhydrophobic surface via atmospheric air dielectric barrier discharge (DBD) with sealed discharge zone. Siloxane monomers along with silica nanoparticles were used to construct micro-scale hierarchical morphology in gas phase. It is verified that the water repellency of sample could be regulated through adjusting volume and air humidity of discharge zone. The generated reactive oxygen species induced polymerization of long-chain alkyl silane and also caused the grafting of polar groups on substrate surface. Within 5 min, the long-chain alkyl silane coating could rapidly wrap silica nanoparticles layer-by-layer to form microspheres and hence the micro-scale hierarchical morphology. The discharge zone with appropriate sealing volume could balance the grafting amount of polar and nonpolar groups to optimize surface hydrophobicity. After repeating the plasma treatment three times, the sample possessed superhydrophobicity and excellent performance in water-in-oil emulsion separation. The study may offer an environment-friendly method to prepare water-repellent materials for industrial applications.