Superhydrophobic surfaces with tunable water adhesion have attracted much interest in fundamental research and practical applications. In this paper, we used a simple method to fabricate superhydrophobic surfaces with tunable water adhesion. Periodic microstructures with different topographies were fabricated on copper surface via femtosecond (fs) laser irradiation. The topography of these microstructures can be controlled by simply changing the scanning speed of the laser beam. After surface chemical modification, these as-prepared surfaces showed superhydrophobicity combined with different adhesion to water. Surfaces with deep microstructures showed self-cleaning properties with extremely low water adhesion, and the water adhesion increased when the surface microstructures became flat. The changes in surface water adhesion are attributed to the transition from Cassie state to Wenzel state. We also demonstrated that these superhydrophobic surfaces with different adhesion can be used for transferring small water droplets without any loss. We demonstrate that our approach provides a novel but simple way to tune the surface adhesion of superhydrophobic metallic surfaces for good potential applications in related areas.

Realizing superhydrophobicity, high transparency on polydimethylsiloxane (PDMS) surface enlarges its application fields. We applied a femtosecond laser to fabricate well-designed structures combining microgrooves with microholes array on mirror finished stainless steel to form a template. Then liquid PDMS was charged for the duplicating process to introduce a particular structure composed of a microwalls array with a certain distance between each other and a microprotrusion positioned at the center of a plate surrounded by microwalls. The parameters such as the side length of microwalls and the height of a microcone were optimized to achieve required superhydrophobicity at the same time as high-transparency properties. The PDMS surfaces show superhydrophobicity with a static contact angle of up to 154.5 ± 1.7° and sliding angle lower to 6 ± 0.5°, also with a transparency over 91%, a loss less than 1% compared with plat PDMS by the measured light wavelength in the visible light scale. The friction robust over 100 cycles by sandpaper, strong light stability by 8 times density treatment, and thermal stability up to 325 °C of superhydrophobic PDMS surface was investigated. We report here a convenient and efficient duplicating method, being capable to form a transparent PDMS surface with superhydrophobicity in mass production, which shows extensive application potentials.

The Cassie-state stability plays a vital role in the applications of metallic superhydrophobic surfaces. Although a large number of papers have reported the superhydrophobic performance of various surface micro/nanostructures, the knowledge of which kind of micro/nanostructure contributes significantly to the Cassie-state stability especially under low temperature and pressure is still very limited. In this article, we fabricated six kinds of typical micro/nanostructures with different topography features on metal surfaces by a femtosecond laser, and these surfaces were modified by fluoroalkylsilane to generate superhydrophobicity. We then systematically studied the Cassie-state stability of these surfaces by means of condensation and evaporation experiments. The results show that some superhydrophobic surfaces, even with high contact angles and low sliding angles under normal conditions, are unstable under low temperature or external pressure. The Cassie state readily transits to a metastable state or even a Wenzel state under these conditions, which deteriorates their superhydrophobicity. Among the six micro/nanostructures, the densely distributed nanoscale structure is important for a stable Cassie state, and the closely packed micrometer-scale structure can further improve the stability. The dependence of the Cassie-state stability on the fabricated micro/nanostructures and the laser-processing parameters is also discussed. This article clarifies optimized micro/nanostructures for stable and thus more practical metallic superhydrophobic surfaces.

Infrared antireflection is an essential issue in many fields such as thermal imaging, sensors, thermoelectrics, and stealth. However, a limited antireflection capability, narrow effective band, and complexity as well as high cost in implementation represent the main unconquered problems, especially on metal surfaces. By introducing precursor micro/nano structures via ultrafast laser beforehand, we present a novel approach for facile and uniform growth of high-quality oxide semiconductor nanowires on a Cu surface via thermal oxidation. Through the enhanced optical phonon dissipation of the nanowires, assisted by light trapping in the micro structures, ultralow total reflectance of 0.6% is achieved at the infrared wavelength around 17 μm and keeps steadily below 3% over a broad band of 14-18 μm. The precursor structures and the nanowires can be flexibly tuned by controlling the laser processing procedure to achieve desired antireflection performance. The presented approach possesses the advantages of material simplicity, structure reconfigurability, and cost-effectiveness for mass production. It opens a new path to realize unique functions by integrating semiconductor nanowires onto metal surface structures.

droplets to move along the leaf veins and finally to the root, helping the plants to survive. [11] Inspired by rice leaves, several methods have been proposed to fabricate anisotropic groove-like micro-and nanostructures for obtaining superhydrophobic surfaces with anisotropic sliding behavior. [14][15][16][17][18] Comparing to normal microstructures, fabricating such microstructures faces some challenges. The formation of anisotropic groove-like micron-structures with large period and height is really difficult. So most methods use photolithography to prepare micro-grooves, and combine with other methods to form nanostructures. [11,13,[19][20][21] Therefore, these methods are always timeconsuming, expensive, and size-limited. Some other methods, including surface wrinkling, [22,23] self-masking reactive-ion etching, [24] nano-imprinting lithography, [25] and relevant biomimetic fabrication methods [26,27] cannot control the period and height of the surface micro-grooves precisely. Because of the lack of suitable fabrication methods, systematic studies about the influences of anisotropic groove-like microstructures on the anisotropic sliding behavior are insufficient.In this work, we found that the groove-like microstructures and anisotropic sliding behavior of water droplets were also existed on some other plants, such as the reed leaves. To understand more about the anisotropic sliding behavior of water droplets caused by the anisotropic groove-like microstructures, we fabricated periodic groove-like microstructures on metal surfaces by femtosecond laser micromachining. As the flexibility and controllability of this method, we could not only control the period and height of the surface micron-structures, but also regulate the surface nanoscale roughness. We studied the influences of these structural parameters on the anisotropic sliding behavior systematically, and theoretical analyses were conducted to explain the observed phenomena. Results and Discussion Reed LeavesThe surfaces of rice leaves display many parallel micro-grooves. The width and depth of these micro-grooves reach up to about Former studies have found that water droplets on the rice leaves exhibit anisotropic sliding behavior, which is mainly caused by the anisotropic groovelike surface microstructures. Similar groove-like surface microstructures and anisotropic sliding behavior of water droplets can also be found on some other plants, such as the reed leaves. In this paper, biomimetic groove-like surface microstructures are fabricated on copper surfaces by femtosecond laser micromachining. Thanks to the flexibility of this method, the period and height of the periodic micro-grooves can be precisely controlled, and the nanoscale surface roughness can also be regulated. The influences of these surface morphologies on the wetting state and anisotropic sliding behavior of water droplets are studied systematically, and theoretic analyses are also conducted. Our results prove that the anisotropic sliding behavior is mainly decided by the wetting stat...