Effect of channel structure on microchannel emulsification

Microchannel (MC) emulsification is a novel technique for producing monodispersed emulsions in which droplets are formed by spontaneous transformation caused by interfacial tension. An MC structure consists of a narrow channel and a slitlike terrace. In this study, to investigate the effect of the channel structure on the dynamic behavior of droplet formation from an MC, we performed MC emulsification using MCs with different channel widths and lengths and observed emulsification behaviors using a microscope equipped with a high-speed camera. The formed droplet diameter was independent of the channel width and length and was constant below the critical flow velocity, over which the droplet diameter drastically increased. The time for droplet detachment also drastically increased above the critical velocity. It was found that the critical velocity was high for narrow and long channels. It means that droplet formation is based on the spontaneous transformation caused by interfacial tension at high flow velocity using narrow and long channels. Narrow and long channels produce a large pressure drop in the channel. The large pressure drop in the channel may disturb the flow of the dispersed phase in the channel into the well through the terrace during detachment. Therefore, the dispersed phase on the terrace detaches in less time using narrow and long channels. As a result, an MC structure with narrower and longer channels is better for high emulsion production rates.