我是小水滴，我在玩蹦床，你在哪？

普通水滴掉地上不但沒有粉身碎骨，反而越彈越高??？最新一期的Nature文章（doi:10.1038/nature15738）再次挑戰(zhàn)我們的直覺。

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揭秘：

1、小水滴的媽媽在雜貨鋪給他買了張蹦床（圖a插畫），這張蹦床能保護(hù)小水滴不被摔壞。

2、小水滴玩之前黃豆吃得不少，每次觸床那會兒就忍不住要……

題目Spontaneous droplet trampolining on rigid superhydrophobic surfaces
作者Thomas m. Schutzius1*, Stefan Jung1*, Tanmoy maitra1, Gustav Graeber1, moritz K?hme1 & Dimos Poulikakos1
摘要Spontaneous removal of condensed matter from surfaces is
exploited in nature and in a broad range of technologies to achieve
self-cleaning1,2, anti-icing3–6 and condensation control7,8. But
despite much progress5–7,9–14, our understanding of the phenomena leading to such behaviour remains incomplete, which makes
it challenging to rationally design surfaces that benefit from its
manifestation15–18. Here we show that water droplets resting on
superhydrophobic textured surfaces in a low-pressure environment
can self-remove through sudden spontaneous levitation and subsequent trampoline-like bouncing behaviour, in which sequential
collisions with the surface accelerate the droplets. These collisions
have restitution coefficients (ratios of relative speeds after and
before collision) greater than unity19 despite complete rigidity of
the surface, and thus seemingly violate the second law of thermodynamics. However, these restitution coefficients result from an
overpressure beneath the droplet produced by fast droplet vaporization while substrate adhesion and surface texture restrict vapour
flow. We also show that the high vaporization rates experienced
by the droplets and the associated cooling can result in freezing
from a supercooled state20,21 that triggers a sudden increase in
vaporization, which in turn boosts the levitation process. This
effect can spontaneously remove surface icing by lifting away
icy drops the moment they freeze. Although these observations
are relevant only to systems in a low-pressure environment, they
show how surface texturing can produce droplet–surface interactions that prohibit liquid and freezing water-droplet retention
on surfaces.