Satpathi N S, Nampoothiri K N, Sen A K
Micro Nano Bio Fluidics Unit, Fluid Systems Laboratory, Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai - 600036, Tamil Nadu, India.
Micro Nano Bio Fluidics Unit, Fluid Systems Laboratory, Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai - 600036, Tamil Nadu, India.
J Colloid Interface Sci. 2023 Jul;641:499-509. doi: 10.1016/j.jcis.2023.03.058. Epub 2023 Mar 11.
Surface acoustic waves (SAW) propagating along a solid surface can significantly affect the dynamics of droplet impact. Although droplet impact in presence of SAW has been attempted recently, here, we investigate the effects of surface wettability, droplet size, impact velocity, and SAW power on the impact and spreading dynamics along with post-impact oscillation dynamics of a drop.
Here, we study droplet impact on a surface exposed to traveling SAW produced using an interdigitated electrode patterned on a piezoelectric substrate. The effects of Weber number (We), surface wettability, and SAW power on the impact and spreading dynamics and post-impact oscillation dynamics are studied.
Our study unravels that the interplay between capillary and viscous forces, and inertia forces arising due to pre-impact kinetic energy and SAW-induced bulk acoustic streaming underpins the phenomena. Remarkably, we find that the effect of SAW on droplet impact dynamics is predominant in the case of a hydrophilic (HPL) substrate at a higher SAW power and smaller We and hydrophobic (HPB) substrate irrespective of SAW power. Our study reveals that the maximum droplet spreading diameter increases with SAW power at smaller We for an HPL surface whereas it is independent of SAW power at higher We. Post-impact oscillation of a droplet over an HPL surface is found to be overdamped with a smaller amplitude compared to an HPB substrate, and a faster decay in oscillation amplitude is observed in the case of an HPB surface and higher We. Our study provides an improved understanding of droplet impact on a surface exposed to SAW that may find relevance in various practical applications.
沿固体表面传播的表面声波（SAW）会显著影响液滴撞击的动力学。尽管最近有人尝试研究存在表面声波时的液滴撞击情况，但在此我们研究表面润湿性、液滴大小、撞击速度和表面声波功率对液滴撞击及铺展动力学以及撞击后振荡动力学的影响。
在此，我们研究液滴撞击在一个暴露于由压电基片上的叉指电极产生的行波表面声波的表面上的情况。研究了韦伯数（We）、表面润湿性和表面声波功率对撞击及铺展动力学以及撞击后振荡动力学的影响。
我们的研究表明，毛细力与粘滞力之间的相互作用，以及由撞击前动能和表面声波诱导的体声流产生的惯性力是这些现象的基础。值得注意的是，我们发现，在较高表面声波功率和较小韦伯数的情况下，对于亲水（HPL）基片，表面声波对液滴撞击动力学的影响占主导地位；而对于疏水（HPB）基片，无论表面声波功率如何，这种影响都占主导地位。我们的研究表明，对于HPL表面，在较小韦伯数时，最大液滴铺展直径随表面声波功率增加而增大，而在较高韦伯数时，它与表面声波功率无关。发现在HPL表面上的液滴撞击后振荡是过阻尼的，与HPB基片相比振幅较小，并且在HPB表面和较高韦伯数的情况下，观察到振荡振幅的衰减更快。我们的研究增进了对液滴撞击暴露于表面声波的表面的理解，这可能在各种实际应用中具有相关性。
