Micro/Nanophysics Research Laboratory, School of Electrical and Computer Engineering, RMIT University, Melbourne, Victoria 3000, Australia.
Nat Commun. 2012;3:1167. doi: 10.1038/ncomms2168.
Acoustic-fluid interactions not only has had a long history but has recently experienced renewed scrutiny because of their vast potential for microscale fluid and particle manipulation. Here we unravel a fascinating and anomalous ensemble of dynamic 'acoustowetting' phenomena in which a thin film drawn from a sessile drop first spreads in opposition to the acoustic wave propagation direction. The advancing film front then exhibits fingering instabilities akin to classical viscous fingering, but arising through a different and novel mechanism: transverse Fresnel diffraction of the underlying acoustic wave. Peculiar 'soliton-like' wave pulses are observed to grow above these fingers, which, on reaching a critical size, translate away along the wave propagation direction. By elucidating the complex hydrodynamics underpinning the spreading, and associated flow reversal and instability phenomena, we offer insight into the possibility of acoustically controlling fast and uniform film spreading, constituting a flexible and powerful alternative for microfluidic transport.
声流相互作用不仅历史悠久，而且由于其在微尺度流体和颗粒操纵方面的巨大潜力，最近再次受到关注。在这里，我们揭示了一个引人入胜的、反常的动态“声润湿”现象的集合，其中从静止液滴中提取的薄膜首先在与声波传播方向相反的方向上扩散。然后，前进的薄膜前缘表现出类似经典粘性指进的指进不稳定性，但产生的机制不同且新颖：底层声波的横向菲涅耳衍射。在这些指状物上方观察到奇特的“类孤子”波脉冲生长，当达到临界尺寸时，它们沿着波传播方向平移。通过阐明支撑扩展的复杂流体动力学以及相关的流动反转和不稳定性现象，我们深入了解了声控快速和均匀薄膜扩展的可能性，为微流控传输提供了一种灵活而强大的替代方案。
