Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai, 600036, India.
Soft Matter. 2018 Jan 31;14(5):725-733. doi: 10.1039/c7sm02068f.
We report the continuous splitting of aqueous droplets at the interface between two co-flowing immiscible oil streams in a microchannel. The aqueous droplets initially present in a primary continuous stream (CP) migrate into a secondary continuous stream (CP) when the ratio of the non-inertial lift force to the interfacial tension force exceeds a critical value (K. S. Jayaprakash, U. Banerjee and A. K. Sen, Langmuir, 2016, 32, 2136-2143). Here, experiments were performed to understand the droplet splitting phenomenon and demonstrate the splitting of droplets encapsulating microbeads and cells. The results showed that the droplet splitting phenomenon is governed by the capillary number Ca, which is a function of the average shear stress across the channel, interfacial tension σ between the CP and the droplet phase and the droplet length-scale L. Irrespective of the individual values of these parameters, droplet splitting was observed when the capillary number Ca exceeds a critical value Ca, which was found to be a function of droplet to CP viscosity ratio λ. The Ca was found to be minimum for λ ≈ 1 but higher for droplets of λ ≫ 1 and λ ≪ 1. The sizes of the primary and secondary daughter and migrated droplets (i.e. L and L) were found to increase linearly with the increase in the size of the primary or secondary parent droplets (L). Splitting of parent droplets encapsulating a single microbead or PBMC showed that after splitting, the presence of the microbead or PBMC in the daughter or migrated droplets depends on the ratio of the size of the migrated droplets to that of the parent droplet (i.e. V/V). Finally, splitting of parent droplets containing two or more microbeads or cells into droplets containing a single particle or cell was demonstrated. A new paradigm of droplet splitting is reported that could find applications in soft matter and single-cell studies.
我们报告了在微通道中两股不相容的油流共流界面处，水相液滴的连续分裂。当非惯性升力与界面张力的比值超过临界值（K. S. Jayaprakash、U. Banerjee 和 A. K. Sen，Langmuir，2016，32，2136-2143）时，最初存在于主连续流（CP）中的水相液滴迁移到次连续流（CP）中。在这里，进行了实验以了解液滴分裂现象，并演示了包裹微珠和细胞的液滴的分裂。结果表明，液滴分裂现象受毛细数 Ca 控制，Ca 是通道内平均剪切应力、CP 和液滴相之间的界面张力σ和液滴长度尺度 L 的函数。无论这些参数的个体值如何，当毛细数 Ca 超过临界值 Ca 时，观察到液滴分裂，而 Ca 被发现是液滴与 CP 粘度比 λ的函数。对于 λ≈1，Ca 最小，但对于 λ≫1 和 λ≪1 的液滴，Ca 更高。母液滴分裂成的子液滴和迁移液滴（即 L 和 L）的尺寸与母液滴（L）的尺寸呈线性增加。含有单个微珠或 PBMC 的母液滴的分裂表明，分裂后，微珠或 PBMC 是否存在于子液滴或迁移液滴中取决于迁移液滴与母液滴的尺寸比（即 V/V）。最后，演示了含有两个或更多微珠或细胞的母液滴分裂成含有单个颗粒或细胞的液滴。报告了一种新的液滴分裂范例，它可能在软物质和单细胞研究中得到应用。
