Wang Jinqing, Zhang Muan, Liu Wei, Kong Ming, Zhan Mingxiu, Wu Xuhui, Wu Hao, Feng Zhi, Xu Xu
The Institute for Energy Engineering, China Jiliang University, Hangzhou 310018, P. R. China.
Langmuir. 2024 Jan 30;40(4):2039-2049. doi: 10.1021/acs.langmuir.3c02680. Epub 2024 Jan 18.
Digital holography, recognized for its noncontact nature and high precision in three-dimensional imaging, is effectively employed to measure the morphology of bubbles and droplets. However, in terms of near-wall bubbles and droplets, such as confined bubbles in microfluidic chips, the measurement of the interface morphology of bubbles near the glass surface has not yet been resolved due to the coherent noise resulting from glass surface reflections in microfluidic chips. Accordingly, an off-axis digital holography system was devised by using Linnik interferometry. Measuring the confined bubble interface near the wall within a microfluidic chip and droplet evaporation on solid surfaces was studied. Partially coherent LED sources and reference light modulation techniques were employed in the optical setup to mitigate the coherent noise. Dual exposure and weighted least-squares unwrapping algorithms were introduced to correct phase distortions, enhancing image quality. Imaging two confined CO bubbles was done near the wall in silicon oil within a porous microfluidic chip, and contact angles of 4.7 and 4.5° were measured. Additionally, the measurement of the three-dimensional morphology of vertically evaporating deionized water droplets on a glass surface was done, due to which calculation of contact angles at various orientations was possible. This work offers a feasible new method for measuring the 3D interface morphology of bubbles and droplets, particularly in microfluidic visualization, addressing current measurement gaps.
数字全息术因其非接触特性和三维成像的高精度而闻名，被有效地用于测量气泡和液滴的形态。然而，对于近壁气泡和液滴，如微流控芯片中的受限气泡，由于微流控芯片中玻璃表面反射产生的相干噪声，玻璃表面附近气泡的界面形态测量尚未得到解决。因此，通过使用林尼克干涉测量法设计了一种离轴数字全息系统。研究了测量微流控芯片内靠近壁面的受限气泡界面以及固体表面上的液滴蒸发情况。在光学装置中采用部分相干发光二极管光源和参考光调制技术来减轻相干噪声。引入双曝光和加权最小二乘解包裹算法来校正相位畸变，提高图像质量。在多孔微流控芯片内的硅油中靠近壁面成像了两个受限的CO气泡，并测量了4.7°和4.5°的接触角。此外，还对玻璃表面上垂直蒸发的去离子水滴的三维形态进行了测量，据此可以计算不同取向的接触角。这项工作为测量气泡和液滴的三维界面形态提供了一种可行的新方法，特别是在微流控可视化方面，填补了当前的测量空白。
