Cheng Yuxuan, Lonial Benjamin F, Sista Shivnag, Meer David J, Hofert Anisa, Weeks Eric R, Shattuck Mark D, O'Hern Corey S
Department of Physics, Yale University, New Haven, Connecticut, 06520, USA.
Department of Physics, Emory University, Atlanta, GA 30322, USA.
Soft Matter. 2024 Oct 16;20(40):8036-8051. doi: 10.1039/d4sm00752b.
Capillary droplets form due to surface tension when two immiscible fluids are mixed. We describe the motion of gravity-driven capillary droplets flowing through narrow constrictions and obstacle arrays in both simulations and experiments. Our new capillary deformable particle model recapitulates the shape and velocity of single oil droplets in water as they pass through narrow constrictions in microfluidic chambers. Using this experimentally validated model, we simulate the flow and clogging of single capillary droplets in narrow channels and obstacle arrays and find several important results. First, the capillary droplet speed profile is nonmonotonic as the droplet exits the narrow orifice, and we can tune the droplet properties so that the speed overshoots the terminal speed far from the constriction. Second, in obstacle arrays, we find that extremely deformable droplets can wrap around obstacles, which leads to decreased average droplet speed in the continuous flow regime and increased probability for clogging in the regime where permanent clogs form. Third, the wrapping mechanism causes the clogging probability in obstacle arrays to become nonmonotonic with surface tension . At large , the droplets are nearly rigid and the clogging probability is large since the droplets can not squeeze through the gaps between obstacles. With decreasing , the clogging probability decreases as the droplets become more deformable. However, in the small- limit, the clogging probability increases since the droplets are extremely deformable and wrap around the obstacles. The results from these studies are important for developing a predictive understanding of capillary droplet flows through complex and confined geometries.
当两种互不相溶的流体混合时，由于表面张力会形成毛细管液滴。我们通过模拟和实验描述了重力驱动的毛细管液滴在狭窄通道和障碍物阵列中的流动。我们新的毛细管可变形粒子模型概括了单个油滴在水中通过微流控腔室中的狭窄通道时的形状和速度。利用这个经过实验验证的模型，我们模拟了单个毛细管液滴在狭窄通道和障碍物阵列中的流动和堵塞情况，并得到了几个重要结果。首先，当液滴离开狭窄孔口时，毛细管液滴速度分布是非单调的，并且我们可以调整液滴特性，使得速度在远离收缩处时超过终端速度。其次，在障碍物阵列中，我们发现极易变形的液滴可以缠绕在障碍物周围，这导致在连续流动状态下平均液滴速度降低，并且在形成永久性堵塞的状态下堵塞概率增加。第三，缠绕机制导致障碍物阵列中的堵塞概率随表面张力变得非单调。在表面张力较大时，液滴几乎是刚性的，堵塞概率较大，因为液滴无法挤过障碍物之间的间隙。随着表面张力减小，由于液滴变得更易变形，堵塞概率降低。然而，在表面张力极小的情况下，堵塞概率增加，因为液滴极易变形并缠绕在障碍物周围。这些研究结果对于建立对毛细管液滴在复杂受限几何结构中流动的预测性理解非常重要。
