Superrepellency of underwater hierarchical structures on Salvinia leaf

Abstract

Biomimetic superhydrophobic surfaces display many excellent underwater functionalities, which attribute to the slippery air mattress trapped in the structures on the surface. However, the air mattress is easy to collapse due to various disturbances, leading to the fully wetted Wenzel state, while the water filling the microstructures is difficult to be repelled to completely recover the air mattress even on superhydrophobic surfaces like lotus leaves. Beyond superhydrophobicity, here we find that the floating fern, Salvinia molesta, has the superrepellent capability to efficiently replace the water in the microstructures with air and robustly recover the continuous air mattress. The hierarchical structures on the leaf surface are demonstrated to be crucial to the recovery. The interconnected wedge-shaped grooves between epidermal cells are key to the spontaneous spreading of air over the entire leaf governed by a gas wicking effect to form a thin air film, which provides a base for the later growth of the air mattress in thickness synchronously along the hairy structures. Inspired by nature, biomimetic artificial Salvinia surfaces are fabricated using 3D printing technology, which successfully achieves a complete recovery of a continuous air mattress to exactly imitate the superrepellent capability of Salvinia leaves. This finding will benefit the design principles of water-repellent materials and expand their underwater applications, especially in extreme environments.

The challenges, achievements and applications of submersible superhydrophobic materials

“…71,90 As this plant lives on the surface of the water, its air-retention ability becomes important when accidentally immersed in water to maintain its respiration and photosynthesis processes. 76 This has been attributed to the external layer of densely packed hairlike features on the leaf surface (Fig. 6h).…”

“…self-cleaning of Lotus leaves), as well as the ability to maintain an air layer while underwater for different periods, depending on their needs. 71,[74][75][76][77][78] As many insects have life cycles connected to water, their bodies have evolved accordingly to repel water, which is necessary for their breathing and additional functionality. 77 A thorough examination of surfaces found in nature reveals key design features required for airlayer stability underwater.…”

Natural Architectures for Tissue Engineering and Regenerative Medicine

“…Likewise, another study reported the ability of sixteen reproduced plant surfaces to affect the spatial distribution of Pseudomonas aeruginosa attachment [ 63 ]. Superhydrophobic characteristics of plants are also exploited for self-cleaning and drag-reducing effects [ 81 , 82 ]. For example, Xiang et al [ 81 ] fabricated a biomimetic Salvinia molesta surface using a 3D printing approach, which imitates the floating fern’s superrepelent capability.…”

“…Superhydrophobic characteristics of plants are also exploited for self-cleaning and drag-reducing effects [ 81 , 82 ]. For example, Xiang et al [ 81 ] fabricated a biomimetic Salvinia molesta surface using a 3D printing approach, which imitates the floating fern’s superrepelent capability. Similarly, the rice leaf anisotropic structure has been implemented for such properties [ 82 ].…”

Air Retention under Water by the Floating Fern Salvinia: The Crucial Role of a Trapped Air Layer as a Pneumatic Spring

“…Therefore, the surface of Salvinia leaves is considered as a biological model for technological air-retaining surfaces. [5,[40][41][42][43][44][45][46][47][48][49] In order to have an effective air retention, the upper side of the leaves is covered with elastic, superhydrophobic, eggbeater-shaped trichomes (later called "hairs") (see Figure 1a,b). The backside of the leaf is hydrophilic, and therefore staying in permanent direct contact with water.…”