Large-area Metal Lotus-like Structures Fabricated By Picosecond Laser For Superhydrophobic Surface Replication

The self-cleaning superhydrophobic surfaces will be able to repel water, dust andcontaminant for various potential applications in industrial production and daily life. Tomimic the surface structures of lotus leaves, many advanced technologies have beendeveloped for the formation of micro/nano hierarchical surface structures. Artificialsuperhydrophobic surfaces are being realized on polymers, semiconductor materials andmetals, which have met the needs for experimental researches. However, novel costeffective methods for mass production and commercial application are still sharplyneeded.In this thesis, a methodology combining picosecond laser ablation of metal withmicro/nano imprinting technique to produce superhydrophobic surfaces is demonstratedprecisely. Specifically, the metal molds are effectively fabricated by picosecond laserwhile the imprinting technique and replicas are all industrial available, with the aim tostudy the feasibility and practicality of such methodology in industrial applications.Picosecond laser ablation is one of the advanced way to rapidly prepare micro/nanosurface structures. By cautiously controlling the laser parameters, surface nanostructures, micro structures or micro/nano hierarchical structures are all highly availablethrough picosecond laser fabrication. With the design of a imprinting mold matching thelotus leaf, high-power&high-repetition-rate picosecond laser is used to fabricate microcraters onto the surfaces of high speed tool steel and mold steel. The surface craters areformed in a hexagonal array while abundant nano structures are formed at thesame time inside the craters. Using the optimized parameters, metal molds arerapidly fabricated with negative lotus-leaf micro/nano hierarchical structures in alarge area.Such molds serve as replication master surfaces during the aluminum alloy castingprocedure to test their ability to work under high temperature and high pressure, and torealize the replication of micro/nano structures onto metal surface. Large number offrustoconical bumps are formed, decorated by secondary step-like asperity onthe sides, onto the aluminum alloy surface. As a result, the contact anglemeasurement shows that the aluminum alloy is tuned form hydrophilic to hydrophobic.Besides, silicone rubber hot-press vulcanization process is also performed torealize cost effective fabrication of highly roughened silicone rubber under mediumtemperature and pressure conditions. Lotus-like silicone rubber surfaces are successfullyobtained by replication and the formation of micro protuberance arrays and fine nanowave-like structures on the protuberance. The contact angle of such kind ofsurface is tested to be155.5°with a fairly low hysteresis of about1.42°.Therefore, the imprinted surfaces show important potential for industrialsilicone rubber insulators applications.