A Floating Capillary Based Open Microfluidic Device for Stable and On- Demand Generation of Monodispersed Emulsion Droplets

Simple and stable generation of monodispersed droplets with volume from picolitre to nanoliter is one of the key factors in high-throughput quantitative microreactors for chemical and biomedical applications. In this work, a floating capillary based open microfluidic device (FCOMD) is constructed by inserting a capillary with an oblique angle (α) into the continuous phase (CP) to develop a simple method for preparation of monodispersed droplet. The geometrical parameters, including inner diameter and α, present a strong correlation for the controllability of droplet breakage and thus its volume. According to the microfluidic experiments, the mechanism of breakup of dispersed phase (DP) into droplets in the FCOMD was proposed from the aspect of energy. The transition of droplet generating mode between dripping and jetting can be achieved by changing the DP capillary number and α. Water in oil (W/O), oil in water (O/W), double-emulsion, colloidal dispersed droplets and liquid crystal droplets with diameter ranges from 25–800 µm (CVs under 2%) are prepared on-demand by the FCOMD. To improve the generating throughput, different numbers of capillaries are integrated for an integrated FCOMD. This FCOMD shows the features of simple, stable, practicable, and flexible, showing a great potential application in material science, foods, pharmaceuticals and cosmetics.