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(Color online) Device geometry and droplet mechanics. (a) Device geometry. Microfluidic device consists of multiple chambers connected by thin necks. Flow streamlines are shown in this illustration to indicate the path taken by the water when injected into an oil-filled device. Generally, water only passes along the central regions. Highest velocity regions are shaded dark gray. [(b)–(d)] Video frames showing how droplets are formed. Video frame (b) was taken during the injection of fluid into the oil-filled device. Video frames (c) and (d) were taken after injection had stopped. They show how instabilities (pinch points) form in the aqueous solution at the neck regions under static conditions, followed by pullback by the drop into the main chamber. The hydraulic slot allows oil to be displaced from the main chamber as the water drop forms.
(Color online) Droplet dependence on injection flow and viscosity. Droplet formation in 15 chambers was monitored for different injection flow rates and aqueous viscosities. Average volumes are plotted for the trials. Also shown are representative video images to indicate the nature of the drops. For low flow rates and high flow rates, droplet formation was not stable.
(Color online) Droplet dependence on chamber geometry. Droplet formation in 15 chambers was monitored for different chamber sizes. The corrected chamber length was varied. Chamber width was scaled proportionately. Water was injected at . Average droplet volumes are plotted, and the solid curve represents predicted volumes according to the design formula. Also shown are representative video frames that show the droplets in different sized chambers.
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