This paper aims to investigate a mechanism of microdroplet formation using "multicolor confocal micro particle image velocimetry (PIV)" technique. This system consists of a conventional confocal micro PIV system and multicolor separation optics, which utilize two lasers for illumination and record fluorescent light at two distinct wavelengths. In order to capture clear particle images and eliminate unnecessary scattering light, the optical components (e.g., filters and dichroic mirror) are chosen based on their optical properties. The new system can measure dynamical behavior of multiphase flow separately and simultaneously. It also enables to identify the interactions between different phases such as 'solid-liquid' or 'liquid-liquid'. We have applied this system to measure the water droplet formation in surrounding oil phase at a micro T-shaped junction. We have also succeeded to disperse fluorescent tracer particles into both phases. The interaction between the internal flow of to-be-dispersed aqueous phase and that of continuous oil phase are measured as a liquid-liquid multiphase flow. As a result, the interactions involved in biphasic interfaces show the flow structure of squeezing, dripping and circulation motion inside each phases depending on the Capillary number.

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