Quintero R, Simonetti F
School of Aerospace Systems, University of Cincinnati, Cincinnati, Ohio 45221, USA.
Phys Rev E Stat Nonlin Soft Matter Phys. 2013 Oct;88(4):043011. doi: 10.1103/PhysRevE.88.043011. Epub 2013 Oct 24.
Radiation of energy by large-amplitude leaky Rayleigh waves is regarded as one of the key physical mechanisms regulating the actuation and manipulation of droplets in surface acoustic wave (SAW) microfluidic devices. The interaction between a SAW and a droplet is highly complex and is presently the subject of extensive research. This paper investigates the existence of an additional interaction mechanism based on the propagation of quasi-Stoneley waves inside sessile droplets deposited on a solid substrate. In contrast with the leaky Rayleigh wave, the energy of the Stoneley wave is confined within a thin fluid layer in contact with the substrate. The hypothesis is confirmed by three-dimensional finite element simulations and ultrasonic scattering experiments measuring the reflection of Rayleigh waves from droplets of different diameters. Moreover, real-time monitoring of the droplet evaporation process reveals a clear correlation between the droplet contact angle and the spectral information of the reflected Rayleigh signal, thus paving the way for ultrasonic measurements of surface tension.
大振幅泄漏瑞利波的能量辐射被视为调节表面声波（SAW）微流控器件中液滴驱动和操控的关键物理机制之一。SAW与液滴之间的相互作用非常复杂，目前是广泛研究的主题。本文研究了一种基于准斯通利波在沉积于固体基板上的静止液滴内传播的额外相互作用机制的存在。与泄漏瑞利波不同，斯通利波的能量局限于与基板接触的薄流体层内。该假设通过三维有限元模拟和测量不同直径液滴对瑞利波反射的超声散射实验得到了证实。此外，对液滴蒸发过程的实时监测揭示了液滴接触角与反射瑞利信号的光谱信息之间的明显相关性，从而为表面张力的超声测量铺平了道路。
