2013年11月21日 Nature* ?' A' m: u: X8 H. q& I; F 3 W6 C# O' ~) ^6 [+ {9 z/ n8 A4 g i
A water drop strikes the water-averse wing of a Morpho % C) [. N5 s7 g7 ~" ^: p) V$ `
butterfly. There are many uses for surfaces that can stay dry, self-clean or % f* D& N: {2 }: t$ i$ }8 z @resist icing. Liquid drops hitting such surfaces tend to spread out and then ' b( A1 }$ `3 h
retract before finally bouncing. Many applications benefit from minimizing the 2 {; \3 q. b+ g( e
contact time between drop and surface, which is generally assumed to occur if ( B! w! {' B3 |4 B
the impacting drop deforms symmetrically. Kripa K. Varanasi and colleagues now # i( } {) x( g9 t) G. I
show that drops bounce off faster from a superhydrophobic surface with a & z! D8 p9 K3 ]- Z, z/ }4 d1 Qmorphology that redistributes the liquid mass so that it no longer spreads and $ w2 O+ \8 |* q3 Z! y
retracts symmetrically. Theory and experiments confirm that this strategy 7 ~) F5 I5 f6 f, e
shortens the contact time between a bouncing drop and a surface beyond what was 9 K& C7 v/ X Q& o* @) f# i( D! othought possible. Photo: A. T. Paxson, K. Hounsell, J. W. Bales, J. C. Bird 5 r- ?% b- d% x7 T! U& K. Varanasi. # J" |. s# a" f# V- ^; p' h- l0 P/ r$ w$ c, w9 y
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