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 (CP₁) migrate into a secondary continuous stream (CP₂) 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 CP₁ 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_cr, which was found to be a function of droplet to CP₂ viscosity ratio λ. The Ca_cr 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_p|sD and L_p|sM) were found to increase linearly with the increase in the size of the primary or secondary parent droplets (L_p|sP). 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_M/V_P). 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.

中文翻译：

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水滴在微通道中并流的不混溶油流的界面处连续分裂†

我们报告了在微通道中的两个同流不混溶油流之间的界面处的水滴的连续分裂。当非惯性升力与界面张力之比超过临界值时（KS Jayaprakash，U. Banerjee），最初存在于主连续流（CP ₁）中的水滴会迁移到第二连续流（CP ₂）中。和AK森，朗缪尔，2016年，32，2136–2143）。在这里，进行实验以了解液滴分裂现象，并演示封装微珠和细胞的液滴分裂。结果表明，液滴分裂现象是由毛细管数Ca决定的，毛细管数Ca是整个通道的平均切应力，CP ₁与液滴相之间的界面张力σ和液滴长度尺度L的函数。不管这些参数的各个值如何，当毛细管数Ca超过临界值Ca _cr时，都会观察到液滴分裂，这是液滴与CP ₂粘度比λ的函数。钙_CR被发现是最小为λ听，说：1，但对于更高的液滴λ »1和λ «1.初级和次级女儿的大小和迁移的液滴（即，大号_{P |±标准差}和大号_{P | SM}）被发现线性增加随着初级或次级母体液滴（L _{p | sP}）尺寸的增加。封装单个微珠或PBMC的母滴的分裂表明，分裂后，子珠或迁移液滴中微珠或PBMC的存在取决于迁移的液滴与母滴的大小之比（即V _M / V _P）。最后，证明了将包含两个或更多个微珠或细胞的亲代液滴分裂为包含单个颗粒或细胞的液滴。据报道，液滴分裂的新范式可以在软物质和单细胞研究中找到应用。