Abstract
A straight-through microchannel (MC) is an array of through-holes microfabricated on a silicon plate. An earlier study reported that a straight-through MC with an oblong section is suitable for preparing monodisperse emulsions by forcing the to-be-dispersed phase into the continuous phase through the MC. This study investigated the effects of the slot aspect ratio and the to-be-dispersed phase flux on the droplet formation from straight-through MCs with equivalent diameters of approximately 20 µm and a depth of 200 µm. Straight-through MCs below a threshold slot aspect ratio of approximately three resulted in the formation of polydisperse droplets, driven by the continuous phase flow. In contrast, straight-through MCs exceeding a threshold slot aspect ratio of approximately three stably yielded monodisperse droplets with average diameters of about 40 µm and coefficients of variation below 3%. The to-be-dispersed phase that grew from these slots was transformed spontaneously into mono-sized droplets. Below the critical to-be-dispersed phase flux, the size and size distribution of the formed monodisperse droplets were almost independent of the to-be-dispersed phase flux. Above the critical to-be-dispersed phase flux, formation of polydisperse large droplets and a drastic increase in the resultant droplet size were observed with an increase in the to-be-dispersed phase flux. A large silicon straight-through MC plate, which measures 40 mm×40 mm×0.4 mm, was developed to scale the emulsification device up. This plate achieved the stable preparation of monodisperse emulsions with maximum droplet productivity of 35 mL/h.
