Song Kui, Zhang Lina, Zhou Zheng, Huang Ruijie, Zheng Xu
College of Civil Engineering and Mechanics, Xiangtan University, Xiangtan 411105, Hunan, China.
State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China.
Biomicrofluidics. 2020 Jul 15;14(4):044105. doi: 10.1063/5.0010175. eCollection 2020 Jul.
Liquid control in microchannels is quite important in microfluidic devices used in, for example, lab-on-a-chip and point-of-care applications. Capillary microfluidics, being self-powered, is especially advantageous for use in passive devices, and has attracted significant attention. In this paper, capillary flows in rectangular microchannels with spacers are studied experimentally and theoretically; in particular, capillary flow synchronization (or waiting) behavior is identified and investigated. Based on changes of channel walls, two basic synchronization modes are proposed for flows isolated by spacers in a channel. Experimental results show that the velocities of faster capillary flows are reduced by the liquid pinning effect and that the time delay between two capillary flows is automatically balanced. The synchronization behavior of capillary flows is explained by analyzing the time delay, contact angle variation, and capillary forces. In addition, the quantity of liquid flowing out of the waiting channels is estimated and verified. Then a model for the change in contact angle during synchronization is derived and verified. Finally, we conceive a series of studies of the control of capillary flows for different spacer designs and conduct an experiment to study the dynamic behaviors of a number of capillary flows by adding many spacers in a microchannel. This study expands the applications of capillary microfluidics.
在诸如芯片实验室和即时护理应用等微流控设备中，微通道内的液体控制非常重要。毛细管微流控技术具有自驱动能力，在无源设备中使用尤其具有优势，因而受到了广泛关注。本文对带有间隔物的矩形微通道中的毛细管流动进行了实验和理论研究；特别地，识别并研究了毛细管流动同步（或等待）行为。基于通道壁的变化，针对通道中被间隔物隔开的流动，提出了两种基本的同步模式。实验结果表明，较快的毛细管流动速度会因液体钉扎效应而降低，并且两个毛细管流动之间的时间延迟会自动平衡。通过分析时间延迟、接触角变化和毛细管力来解释毛细管流动的同步行为。此外，对从等待通道流出的液体量进行了估计和验证。然后推导并验证了同步过程中接触角变化的模型。最后，我们设想了一系列针对不同间隔物设计的毛细管流动控制研究，并通过在微通道中添加多个间隔物来进行实验，以研究多个毛细管流动的动态行为。这项研究拓展了毛细管微流控技术的应用。
