Wettability-confined tracks have been extensively used in open-surface microfluidic devices for their high capacity of transporting droplet pumplessly. Inspired by the experimental work of Sen et al. [ Langmuir 2018 , 34 , 1899 - 1907 ], in the present study, a three-dimensional phase-field lattice Boltzmann model is developed and used to investigate the spreading behaviors of microdroplet on a series of wettability-confined tracks. The experimental findings are successfully reproduced through our simulation, where three distinct stages of droplet spreading on the horizontal wettability-confined diverging track are fairly exhibited, that is, the initial stage with droplet front spreading quickly, the intermediate stage with both droplet front and bulge moving forward at a constant speed, and the final stage with droplet front decelerating gradually. Moreover, a parametric study of track divergence angle is further performed, and the influential mechanism of track divergence angle on droplet spreading is further revealed. It is demonstrated that track divergence is responsible for the Laplace pressure gradient and capillary force inside the droplet, which drives the droplet bulge to move forward on the diverging track. With an increase in divergence angle, the capillary force increases linearly, which increases the droplet spreading speed at the initial and intermediate stages, while the peak capillary force comes earlier, and consequently the final decelerating stage comes earlier. On the basis of the parametric study and droplet volume conservation rule, a power law relation between track divergence angle and droplet spreading is proposed, which helps to identify the start of final decelerating stage. Finally, the droplet spreading over various inclined tracks is explored, which can be achieved only when the capillary force at the beginning is larger than the droplet gravity component along the inclined track surface.

中文翻译：

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使用三维相场格子Boltzmann模型对在润湿性受限的轨道上微滴传播行为的数值研究。

由于可湿性限制的轨道具有无泵输送液滴的高容量，因此已广泛用于开放表面微流控设备中。受Sen等人的实验工作启发。[Langmuir 2018，34，1899-1907]，在本研究中，开发了三维相场晶格玻尔兹曼模型，并用于研究微滴在一系列受润湿性限制的轨道上的扩散行为。通过我们的模拟成功再现了实验结果，其中在水平可湿性限制的发散轨道上散布了三个不同的液滴散布阶段，即液滴散布前期迅速散布的初始阶段，液滴散布前期和凸起的中间阶段以恒定的速度前进，最后阶段液滴前沿逐渐减速。此外，进一步进行了轨道发散角的参数研究，进一步揭示了轨道发散角对液滴扩散的影响机理。事实证明，轨道散度是液滴内部的拉普拉斯压力梯度和毛细作用力的源头，拉普拉斯压力梯度和液滴内的毛细作用力促使液滴鼓起在分散轨道上向前移动。随着发散角的增加，毛细作用力线性增加，从而在初始阶段和中间阶段增加了液滴的扩散速度，而毛细作用力峰值出现的时间更早，因此最终减速阶段发生的时间更早。根据参数研究和液滴体积守恒定律，提出了轨道发散角与液滴扩散之间的幂律关系，有助于确定最终减速阶段的开始。最后，探索液滴散布在各种倾斜轨道上的情况，只有当开始时的毛细力大于沿着倾斜轨道表面的液滴重力分量时，才能实现此目标。