Rapid automatic creation of monodisperse emulsion droplets by microfluidic device with degassed PDMS slab as a...

We previously developed a technique that enabled automatic creation of monodisperse water-in-oil droplets with the use of an air-evacuated PDMS microfluidic device. Although the device generated droplets over a long-time period, the production rate was slow (∼10 droplets per second). In the current study, we aimed to improve this rate, using the same fluid pumping principle described in our previous work, by remodeling our device configuration. To achieve this aim, we developed a new device with a much larger PDMS surface area-to-volume ratio within the air-trapping void space (178 cm^-1 ), than that of our earlier device (5.0 cm^-1 ). This design approach was based on the idea that a larger PDMS surface area-to-volume ratio was likely to create a higher vacuum inside the void space, thereby contributing to faster liquid flow and an increased droplet generation rate. The new device consisting of five layers featuring a degassed PDMS slab as a detachable liquid-suction actuator, which was stacked on a lower microfluidic layer. In this device, the rate of droplet production increased during the time-course droplet formation and reached ca. 470 droplets per second immediately before completely consuming the loaded aqueous solution (20 μL).