We describe the step-by-step formation process of picoliter to femtoliter volume of microdroplets by using a mechanical valve. An experiment-based theoretical model has been proposed through a parametric study of droplet formation in a microchannel with variations of the channel height, the working pressure to drive the liquids in the microchannels, and the viscosity of the dispensed phase. Three steps in the process of droplet generation have been depicted. The present study provides a clear understanding of the droplet generation process based on physical cutting method by using a mechanical valve and could be applied to advanced design for highly flexible dropletbased microfluidic systems. List of symbols P cdFlow pressure in continuous phase and dispensed phase channels P valve (t) Flow pressure in cutter valve channel Q c Flow rate in continuous phase channel Q d Flow rate in dispensed phase channel Q v Flow rate in cutter valve channel R ci

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CorrigendumCorrigendum to < [Chemical Engineering Journal 280 (2015) 385-390]>

We have demonstrated fine control of droplet volumes on a chip using pneumatically actuated micro valve systems resulting in confined nanoliter or picoliter reagent generation. Using the micro valves, we are able to align multi-inlet droplet generating chips for systematic generation of combinatorial mixtures of chemical constituents. By following the change of chemical conditions such as pH we converted musical note information into sequential droplets representing musical scores of 'Twinkle little star.' It would just one of the interesting application of micro-droplet generation systems based on accurate droplet generation, mixing, and incubation. It, thus, would be applied to combinatorial chemical and biological reactions increasing throughput and efficiency with various kinds of reagents.