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Edited by David A. Weitz, Harvard University, Cambridge, MA, and approved December 16, 2019 (received for review January 2, 2019)
Significance
Instability and collapse of the underwater slippery air mattress hinder its applications, after which the air mattress cannot be recovered even on superhydrophobic surfaces like lotus leaves. Beyond superhydrophobicity, we present the underwater superrepellent capacity of Salvinia leaves, which can efficiently and robustly recover the invalid slippery air mattress by trapping the replenished air to replace the water in the microstructures. The interconnected wedge-shaped grooves on the base are key to the recovery, which spontaneously transport the replenished air to the entire surface governed by a gas wicking effect. Using 3D printing technology, biomimetic artificial Salvinia surfaces are fabricated, which successfully achieves the recovery of the air mattress. This finding will greatly extend the underwater applications of water-repellant surfaces.
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.
Footnotes
- ↵1To whom correspondence may be addressed. Email: hlduan{at}pku.edu.cn.
Author contributions: Y. Xiang and H.D. designed research; Y. Xiang, S.H., T.-Y.H., A.D., D.C., H.L., P.L., and H.D. performed research; Y. Xiang analyzed data; and Y. Xiang, S.H., T.-Y.H., Y. Xue, P.L., and H.D. wrote the paper.
The authors declare no competing interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at https://www.pnas.org/lookup/suppl/doi:10.1073/pnas.1900015117/-/DCSupplemental.
Published under the PNAS license.
Superrepellency of underwater hierarchical structures on Salvinia leaf
Article Classifications
- Physical Sciences
- Applied Physical Sciences
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- Article
- Abstract
- In Situ Optical Observation of Air-Mattress Recovery on Submerged Salvinia Leaf
- Microstructures on Salvinia Leaf Surface and the Details of the Air-Mattress Recovery at Microscale
- Mechanism of Air-Mattress Recovery
- Air-Mattress Recovery on Artificial Salvinia Surface: Lessons from Salvinia Leaf
- Conclusion
- Materials and Methods
- Acknowledgments
- Footnotes
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