Role of flexibility in the water repellency of water strider legs: theory and experiment.

Water striders enjoy an intriguing ability to stand and walk freely on water surfaces, which is mainly attributed to the superior water repellency of their slender legs. In previous theoretical analyses, the legs are usually treated as rigid beams and the results show that a tremendously deep dimple and a large supporting force can be achieved when the leg descends into water. In this paper, the effect of the flexibility of water strider legs on their water-repellent ability is investigated, both theoretically and experimentally. We analyze a hydrophobic and flexible leg pressing obliquely on water. The leg may undergo a large deformation and assume different geometric configurations. It is shown that the flexible leg can float easily on a water surface, inducing only a shallow water puddle and a moderate supporting force as observed in real water striders. When the long leg is sufficiently compliant, the water surface will never be pierced and the leg will never sink. The findings are experimentally testified by using flexible fibers to represent water strider legs pressing on water.