Nature-Inspired Superwettability Achieved by Femtosecond Lasers

Abstract

Wettability is one of a solid surface’s fundamental physical and chemical properties, which involves a wide range of applications. Femtosecond laser microfabrication has many advantages compared to traditional laser processing. This technology has been successfully applied to control the wettability of material surfaces. This review systematically summarizes the recent progress of femtosecond laser microfabrication in the preparation of various superwetting surfaces. Inspired by nature, the superwettabilities such as superhydrophilicity, superhydrophobicity, superamphiphobicity, underwater superoleophobicity, underwater superaerophobicity, underwater superaerophilicity, slippery liquid-infused porous surface, underwater superpolymphobicity, and supermetalphobicity are obtained on different substrates by the combination of the femtosecond laser-induced micro/nanostructures and appropriate chemical composition. From the perspective of biomimetic preparation, we mainly focus the methods for constructing various kinds of superwetting surfaces by femtosecond laser and the relationship between different laser-induced superwettabilities. The special wettability of solid materials makes the femtosecond laser-functionalized surfaces have many practical applications. Finally, the significant challenges and prospects of this field (femtosecond laser-induced superwettability) are discussed.

Emerging Separation Applications of Surface Superwettability

“…The lotus leaves rise unstained from the mud because they have a great ability to repel water (Figure 3a). Such a superwetting phenomenon is known as superhydrophobicity [41][42][43][44][45][46][47]. Dewdrops can curl up into a sphere and roll back and forth on a lotus leaf.…”

“…Because the hierarchical surface microstructure dramatically reduces the contact area between the lotus leaf and water, the lotus leaf shows an obvious repulsion to water. The synergistic effect of the hierarchical microstructure and the hydrophobic waxy crystals with low surface energy results in the superhydrophobicity for lotus leaf [41][42][43][44][45][46][47]. Inspired by the lotus leaves, a variety of superhydrophobic materials can be prepared by combining hierarchical microstructure and low-surface-energy chemical components [124][125][126][127][128][129][130][131][132][133][134][135][136][137][138][139][140].…”

“…For the extrema state, superwettability enables the materials to have a significant ability to absorb or repel liquids [36][37][38][39][40]. The lotus leaf with superhydrophobicity is difficult to be wetted by water [41][42][43][44]. Water droplets can easily roll away on the lotus leaf [45][46][47].…”

Design of Metal-Based Slippery Liquid-Infused Porous Surfaces (SLIPSs) with Effective Liquid Repellency Achieved with a Femtosecond Laser

“…A femtosecond (fs) laser, with high peak power and short pulse width, is an on-site processing method that is able to directly create precise micro/nanostructures on almost any material [ 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 ]. Moreover, the process is simple and highly controllable, making it a powerful technique for the construction of SLIPS substrates [ 7 , 31 , 32 , 33 , 34 , 35 ]. Herein, we converted a Gaussian laser beam to the Bessel profile, and the continuous laser pulses were transformed into pulse trains through a method of pulse shaping.…”

Nanoarray-Embedded Hierarchical Surfaces for Highly Durable Dropwise Condensation

“…Therefore, the film-like droplets that pin on the surface will undergo the irreversible Cassie-Wenzel wetting transition, leading to the phenomenon of flooding that declines the heat transfer efficiency of the surface [19,20]. In efforts to maintain the Cassie state of the droplet, previous studies have focused on decreasing the solid-liquid contact area [21,22] or the number of droplet nucleation sites [23,24] by designing increasingly smaller arrays or approximate arrays, from micro to nanoscale size, such as pine needle shapes [6], microconical architectures [25], nanoscaffolds [26], microratchet arrays [27], and vertical arrays of carbon nanotube (CNTs) [28,29]. These surfaces indeed exhibit an enhancement in dropwise condensation by collecting a volume of water three times higher than that in the case of plate surfaces [30], achieving a 100% higher heat flux than that on the plane hydrophobic surface [31], and reaching a directional transport efficiency of approximately 80% for tiny droplets [27].…”