Superhydrophobic surfaces with hydrophilic patterns have great application potential in various fields, such as microfluidic systems and water harvesting. However, many reported preparation methods involve complicated devices and/or masks, making fabrication of these patterned surfaces time-consuming and inefficient. Here, we propose a highly efficient, simple, and maskless microplasma jet (MPJ) treatment method to prepare hydrophilic patterns such as dots, lines, and curves on superhydrophobic aluminum substrates. Contact angles, sliding angles, adhesive forces, and droplet impact behavior of the created patterns are investigated and analyzed. The prepared "dot" patterns exhibit great water adhesion, whereas the "line" patterns show anisotropic adhesion. Additionally, the MPJ treatment does not obviously change the surface structures, which makes it possible to achieve repeatable patterning on one substrate. The adhesion behavior of these patterns could be adjusted using MPJs with different diameters. MPJs with larger diameters are efficient for the creation of patterns with high water adhesion, which can be potentially used for open-channel lab-on-chip systems (e.g., continuous water transportation), whereas MPJs with smaller diameters are preferable in preparing patterns with low water adhesion for diverse applications in biomedical fields (e.g., lossless liquid droplet mixing and cell screening).
Keywords: droplet transportation; hydrophilic pattern; microplasma jet; superhydrophobic aluminum surface; water adhesion.