Roudini Mehrzad, Manuel Rosselló Juan, Manor Ofer, Ohl Claus-Dieter, Winkler Andreas
SAWLab Saxony, Leibniz Institute for Solid State and Materials Research Dresden, Helmholtzstr. 20, Dresden 01069, Germany.
Otto von Guerricke University, Institute for Physics, Universitätsplatz. 2, Magdeburg 39106, Germany.
Ultrason Sonochem. 2023 Aug;98:106530. doi: 10.1016/j.ultsonch.2023.106530. Epub 2023 Jul 24.
The interaction of surface acoustic waves (SAWs) with liquids enables the production of aerosols with adjustable droplet sizes in the micrometer range expelled from a very compact source. Understanding the nonlinear acousto-hydrodynamics of SAWs with a regulated micro-scale liquid film is essential for acousto-microfluidics platforms, particularly aerosol generators. In this study, we demonstrate the presence of micro-cavitation in a MHz-frequency SAW aerosol generation platform, which is touted as a leap in aerosol technology with versatile application fields including biomolecule inhalation therapy, micro-chromatography and spectroscopy, olfactory displays, and material deposition. Using analysis methods with high temporal and spatial resolution, we demonstrate that SAWs stabilize spatially arranged liquid micro-domes atop the generator's surface. Our experiments show that these liquid domes become acoustic resonators with highly fluctuating pressure amplitudes that can even nucleate cavitation bubbles, as supported by analytical modeling. The observed fragmentation of liquid domes indicates the participation of three droplet generation mechanisms, including cavitation and capillary-wave instabilities. During aerosol generation, the cavitation bubbles contribute to the ejection of droplets from the liquid domes and also explain observed microstructural damage patterns on the chip surface eventually caused by cavitation-based erosion.
表面声波（SAWs）与液体的相互作用能够从一个非常紧凑的源产生微米级范围内液滴尺寸可调节的气溶胶。理解具有规则微尺度液膜的表面声波的非线性声流体动力学对于声微流体平台，特别是气溶胶发生器至关重要。在本研究中，我们证明了在兆赫兹频率的表面声波气溶胶生成平台中存在微空化现象，该平台被誉为气溶胶技术的一次飞跃，具有包括生物分子吸入疗法、微色谱和光谱学、嗅觉显示以及材料沉积等广泛的应用领域。使用具有高时间和空间分辨率的分析方法，我们证明表面声波使发生器表面上空间排列的液体微穹顶稳定。我们的实验表明，这些液体微穹顶成为具有高度波动压力振幅的声学谐振器，甚至可以使空化气泡成核，这得到了解析模型的支持。观察到的液体微穹顶破碎表明了三种液滴生成机制的参与，包括空化和毛细波不稳定性。在气溶胶生成过程中，空化气泡有助于从液体微穹顶中喷出液滴，并且还解释了最终由基于空化的侵蚀在芯片表面观察到的微观结构损伤模式。
