Transitions of water-drop impact behaviour on hydrophobic and hydrophilic particles
Transitions of water-drop impact behaviour on hydrophobic and hydrophilic particles
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DOI：
10.1111/ejss.12003
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发表时间：
2013-06-01
影响因子：
4.2
通讯作者：
Newton, M. I.
中科院分区：
文献类型：
--
作者：
Hamlett, C. A. E.;Atherton, S.;Newton, M. I.
极端的土壤排水性可能会对土壤水文、植物生长和侵蚀产生重大影响，包括雨滴撞击造成的飞溅侵蚀加剧。以前对水滴在人造超疏水表面上的撞击行为的研究揭示了三种不同的飞溅行为模式(反弹、钉扎和碎裂)，它们具有两种转变速度：反弹到钉扎(Vmin)和钉扎到碎裂(v*)。通过对单个水滴撞击的高速摄像，我们发现飞溅行为受到静止粒子的疏水性的影响，疏水玻璃球在疏水状态下表现出所有三种飞溅行为模式，而亲水玻璃球只表现出钉扎行为。我们发现，增加固定玻璃球的颗粒大小会增加Vmin。一项关于液滴撞击疏水沙子的研究表明，固定颗粒粗糙度的增加使撞击的液滴更有可能在较慢的冲击速度下破碎。颗粒的流动性影响了液滴的撞击行为，疏水颗粒表现出明显高于其固定类似物的vmin值。水滴的表面张力还将疏水的松散颗粒从表面抬起，形成流动性极强的液体弹珠。在所研究的慢(约0.3-2.1m S-1)和快(约7m S-1)水滴撞击速度下，拒水土壤也能形成液态大理石。观察到非常流动的液体弹珠对水滴对拒水土壤的影响是重要的，因为这提供了一种可能增加拒水土壤侵蚀速率的机制。
Extreme soil water repellency can have substantial implications for soil hydrology, plant growth and erosion, including enhanced splash erosion caused by raindrop impact. Previous studies of water droplet impact behaviour on man-made super-hydrophobic surfaces, with which water-repellent soil shares similar characteristics, revealed three distinct modes of splash behaviour (rebound, pinning and fragmentation) distinguished by two transition velocities: rebound-to-pinning (vmin) and pinning-to-fragmentation (v*). By using high-speed videography of single water droplet impacts we show that splash behaviour is influenced by the hydrophobicity of immobile particles, with hydrophobic glass spheres exhibiting all three modes of splash behaviour in the hydrophobic state but hydrophilic spheres exhibiting solely pinning behaviour. We found that increasing the particle size of fixed glass spheres increases vmin. A study of droplet impact on hydrophobic sand shows that the increased roughness of the immobile particles makes impacting droplets more likely to fragment at slower impact velocities. The mobility of the particles influenced droplet impact behaviour, with loose, hydrophobic particles displaying significantly greater vmin values than their fixed analogues. The surface tension of the water droplet also lifted loose, hydrophobic particles from the surface, forming highly mobile liquid marbles'. Water-repellent soil was also shown to form liquid marbles' at both the slow (approximately 0.3-2.1 m s-1) and fast (about 7 m s-1) droplet impact velocities studied. The observation of very mobile liquid marbles upon water droplet impact on water-repellent soil is significant as this provided a mechanism that may enhance erosion rates of water-repellent soil.