Picosecond laser processing super-wetting surfaces with hierarchical structures for passive driving of microfluidics

Abstract

Hierarchical surfaces with superhydrophilicity have potential applications such as collecting water, liquid transport, and rapid heat transfer, but the fabrication and characterization methods still face challenges. In this paper, hierarchical surfaces with multi-level structures are designed and processed on glass substrates by ultrafast laser writing techniques. The contact angle test results indicate that all processed glass surfaces exhibit superhydrophilicity. To differentiate the hydrophilicity of surfaces with a contact angle approaching 0˚ (CA→0˚), we establish an anti-gravity wetting method characterized by fixed-area wetting time. Compared with laser-roughened glass surfaces, the complete wetting times of surfaces with a three-level-Ⅰ structure were shortened by 51.08 times. The roughness factor of the roughened glass surface increases to r=2.92, confirming the Wenzel model's prediction of enhanced hydrophilicity on rough surfaces. The introduction of sub-millimeter open microgrooves on the roughened surface significantly enhances the ability to transport liquids against gravity through capillary action. Ultimately, the tertiary hierarchical surface achieves the shortest anti-gravity wetting time, indicating the strongest wettability. Microchannels with super-wetting bottom surfaces are constructed and achieve passive rapid driving of microfluidics.