Quasi-static microdroplet production in a capillary trap

TL;DR

This paper presents a capillary trap method for producing microdroplets in oil, controlled by injection volume and frequency, with a theoretical model explaining the process, enabling tunable and low-rate droplet generation.

Contribution

The study introduces a capillary trap technique for microdroplet production with a theoretical model, offering a robust and tunable approach based on capillary and quasi-static principles.

Findings

Droplet size is close to the capillary diameter.

Droplet emission rate is controlled by extraction frequency.

Theoretical model aligns with experimental data.

Abstract

We have developed a method to produce aqueous microdroplets in an oil phase, based on the periodic extraction of a pending droplet across the oil/air interface. This interface forms a capillary trap inside which a droplet can be captured and detached. This process is found to be capillary- based and quasi-static. The droplet size and emission rate are independently governed by the injected volume per cycle and the extraction frequency. We find that the minimum droplet diameter is close to the injection glass capillary diameter and that variations in surface tension moderately perturb the droplet size. A theoretical model based on surface energy minimization in the oil/water/air phases was derived and captures the experimental results. This method enables robust, versatile and tunable production of microdroplets at low production rates.