We introduce the liquid-liquid system to utilize both of the spatial and the temporal localized energy simultaneously by adding temporal localization to microfluidics. Liquid droplets in the gas phase confined in microchannels are used for spatial-temporal localization to realize various chemical processes. A highly accelerated droplet generates the high kinetic energy and momentum in the spatial localization. "Rapid" collision caused by the highly accelerated droplet enables the spatial and temporal localization of the high-energy, which induces the conversion and transfer of the high-energy. We refer to this new microfluidics system as a "micro droplet collider." We fabricated launchers for the droplet shot, tracks for the droplet run, and a chamber for the collision between two droplets on a microchip based on gas-liquid Laplace pressure. The acceleration of the droplet to the high velocity (106 μm s-1; 102 times faster velocity and 104 times higher energy than that of typical water-in-oil droplet format), rapid collision (<100 ls) at a small interface between droplets were achieved. Inelastic and minimally deformable collision was conducted, which enabled the utilization of the localized high-energy efficiently. As one application to chemical processes, we demonstrated rapid mixing (0.5 s) between two droplets (volume ratio; 1 (0.25 nl):10), a process that has not been achieved yet. Mixing time was 6,000 times faster than that of molecular diffusive mixing by utilizing the localized high-energy. The developed micro droplet collider is expected to contribute greatly to microfluidics and chemical processes on a microchip.
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