Parallelization of microfluidic flow-focusing devices

Microfluidic flow-focusing devices offer excellent control over fluid flow, enabling formation of drops with a narrow size distribution. However, the throughput of microfluidic flow-focusing devices is limited and scale-up through operation of multiple drop makers in parallel often compromises the robustness of their operation. We demonstrate that parallelization is facilitated if the outer phase is injected from the direction opposite to that of the inner phase, because the fluid injection flow rate, where the drop formation transitions from the squeezing into the dripping regime, is shifted towards higher values.

Figure 1

(a)–(c) Optical micrographs of microfluidic flow-focusing devices. The angle between the inlet of the outer phase and the main channel, θ, is (a) ${135}^{\circ }$, (b) ${45}^{\circ }$, and (c) ${90}^{\circ }$. (d)–(f) Optical micrographs of drops produced in devices with $\theta =\left(\mathrm{d}\right){135}^{\circ }$, (e) ${45}^{\circ }$, and (f) ${90}^{\circ }$, respectively. The viscosity of the inner phase is 8 mPa s, that of the outer phase is 1 mPa s. The flow rate of the inner phase is 100 μl/h, that of the outer phase is 1 ml/h. Drops have diameters of (a) $75\pm 2\mu \mathrm{m}$, (b) $67\pm 2\mu \mathrm{m}$, and (c) $41\pm 3\mu \mathrm{m}$.

Figure 2

The size of drops produced in devices with $\theta ={45}^{\circ }$ ($•$), ${90}^{\circ }$ ($▴$), and ${135}^{\circ }$ ($\blacksquare$), respectively. The viscosity of the inner phase is 2 mPa s, that of the outer phase is 1 mPa s (filled symbols) and 10 mPa s (open symbols). (a) The influence of the flow rate of the inner phase on the drop size. The flow rate of the outer phase is 1 ml/h. (b), (c) Drop size as a function of the flow rate of the outer phase (b) and the velocity component of the outer phase perpendicular to the main channel (c). The flow rate of the inner phase is 500 μl/h.

Figure 3

The size of drops produced in devices with $\theta =\left(\mathrm{a}\right),\left(\mathrm{d}\right){135}^{\circ }$, (b), (e) ${45}^{\circ }$, and (c), (f) ${90}^{\circ }\mathrm{C}$. The viscosity of the inner phase is 2 mPa s (circles), 8 mPa s (triangles), and 30 mPa s (squares). (a)–(c) The viscosity of the outer phase is 1 mPa s and (d)–(f) 10 mPa s. The flow rate of the outer phase is 1000 μl/h.

Figure 4

Optical micrographs of emulsion drops produced with ten parallelized drop makers operated simultaneously. The angle θ between the outer and inner phase is (a) ${135}^{\circ }$, (b) ${45}^{\circ }$, and (c) ${90}^{\circ }$. The drops have a diameter of (a) $86\pm 3\mu \mathrm{m}(\mathrm{CV}=7\%)$, (b) $64\pm 6\mu \mathrm{m}(\mathrm{CV}=19\%)$, and (c) $86\pm 5\mu \mathrm{m}(\mathrm{CV}=12\%)$.