Dipping microcapillary-based droplet fabrication: Multiscale and structurally diverse droplets with programmable real-time size control

This study presents an innovative “off-chip” droplet manufacturing system, which operates through hydrodynamic interactions between an adjustable flow from a microcapillary and its periodic immersion into a continuous phase. This method circumvents the limitations of conventional microfluidic chips, which are costly and complex to produce, and suffer from restricted control over droplet size. The novel system facilitates the instantaneous alteration of droplet diameters, ranging from approximately one centimeter to several tens of micrometers (77 µm). It employs a slowly rotating continuous phase to prevent droplet agglomeration and precisely manage their sedimentation location. A theoretical model is proposed, linking the radius of the produced droplets to the flow rate of the dispersed phase and the dipping frequency of the microcapillary. This model has been corroborated through computational simulations and empirical experiments. Furthermore, the system has demonstrated proficiency in producing Janus-type and multi-emulsion droplets by simply modifying the geometry of the microcapillary. The absence of microchannel confinement enables the arrangement of droplets into intricate structures, showcasing the system’s unique capacity to utilize both dispersed and continuous phases for creating functional materials with complex multidimensional droplets.