Anisotropic Sliding of Water Droplets on the Superhydrophobic Surfaces with Anisotropic Groove‐Like Micro/Nano Structures

Abstract

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...

Anisotropic silicon nanowire arrays fabricated by colloidal lithography

“…63,64 Furthermore, their anisotropic topography may produce anisotropic wettability and guide the ow of water droplets, comparable to the natural example of the rice leaf, which has a similar morphology. [65][66][67] Last, we demonstrate the fabrication of SiNWs with a crescent-shaped cross-section (Fig. 5).…”

Anisotropic Superhydrophobic Properties of Bioinspired Surfaces by Laser Ablation of Metal Substrate inside Water

“…fabricated groove‐like microstructures on copper surfaces by femtosecond laser micromachining and discussed the wetting state under different conditions. [ 19 ] Li et al. made use of a soft lithography method to prepare oblique two‐tier conical structures under an external magnetic field and realized the directional bouncing of droplets with low energy loss.…”

“…Laser fabrication has been developed to construct superhydrophobic surfaces. [ 19,24–29 ] Although the femtosecond laser is a potential fabrication method owing to its low thermal effect, its poor economy, and low efficiency hinder its applications, [ 30,31 ] while the nanosecond laser has found wide applications in microfabrication processing with much better characteristics of high stability, and high energy. However, the heat accumulation by nanosecond laser scribing and dicing causes significant thermal damage to the substrate.…”

Fabrication of Anti-Reflective Surface with Superhydrophobicity/High Oleophobicity and Enhanced Mechanical Durability via Nanosecond Laser Surface Texturing

“…For example, Vorobyev et al fabricated a multifunctional surface exhibiting combined effects of enhanced light absorption and superhydrophobicity by femtosecond laser texturing [ 28 ]. However, the existing laser-based fabrication techniques rely on the generation of a periodic micro-/nano-scale surface structure with very fine spatial resolution, resulting in relatively low process throughput, which will make it difficult to scale up the process [ 29 , 30 , 31 ]. The high capital cost associated with the ultrashort pulsed lasers also makes the process very expensive [ 28 ].…”