(a) Design of a fixed-volume droplet generator. (b)-(d) Micrographs showing a formation cycle. (b) The dispersed phase injected at a rate, qd , flows into the main channel and blocks it, such that the continuous phase, introduced at a rate, qc , flows around the forming droplet through the bypass. The back of the forming droplet stays at the same location in the T-junction until the front blocks the exit of the bypass (c) resulting in the rapid collapse of the back and the release of a droplet (d). See also the movie in the supplementary material. 11 (e)-(h) Multilayer design of the fixed-volume droplet generator: the bypass is connected to the main channel (depth: h) through a shallow slit (depth: ).
(a) Length of droplets as a function of the ratio of flow rates of the dispersed and the continuous phase. The length, which is normalized by the width of the main channel, corresponds well to the distance between the T-junction and the exitof the bypass channel (Lb ) as indicated by the dashed lines. (b) The formation frequency of the data corresponding to (a) is proportional to the ratio of the flow rate of the dispersed phase and the droplet volume ( ). The standard deviation of the length (a) and frequency (b) data are both below 1% for all data points. Geometries and conditions: ( ) = (100, 25, 150, 42) μm and for and , and ( ) = (100, 25, 150, 24) μm and for .
(a) Multilayer variant of a fixed-volume droplet generator in which the bypass channel is connected to the main channel through a shallow slit. (b) Map of the flow rates of the continuous and dispersed phase showing the deviation of the measured length of the droplets from the reference length . (c) Time-series of the relative drop size and corresponding histogram for a fixed-volume droplet generator (blue dots) and a classic T-junction (red dots). The conditions are indicated by the circle in (b). The average droplet length in the fixed-volume droplet generator and classic T-junction were and respectively. (d) Same as in (c) with conditions indicated by the square in (b). The average length is for both cases. Geometries: fixed-volume droplet generator ( ) = (400, 100, 600, 200,100) μm, classic T-junction (w, h) = (400, 200) μm.
(a) Gravity-driven system for the generation of monodisperse droplets. The continuous phase (CP) is supplied from a wide container such that the rate is constant over the course of the experiment. By contrast, the dispersed phase (DP) is supplied from a tall and narrow container such that the flow rate significantly decreases with time. (b) While the distance between droplets significantly increases over the course of the experiment (blue diamonds), the length of the droplets (red circles) is nearly independent of the pressure head, Hd . The error bars indicate the standard deviation obtained by measuring the length and distance of at least 10 droplets.
(a) Setup for the facile generation of monodisperse droplets containing a solute (ink), whose concentration gradually decreases with time, that is, for successive droplets. Prior to emulsification, a concentrated stream of ink ( ) supplied from a tall and narrow container (DP2) is diluted by mixing it on a separate chip with a stream of solvent supplied from a wide container (DP1). The concentration of this mixture, C, continuously decreases due to a decreasing flow rate of the solute stream caused by a decrease in the pressure head . (b), (c) While the length of the droplets is nearly constant (b), the concentration of ink in the droplets (c) depends on according to , with A, B, D, and E constants, as shown from the excellent agreement between the experimental data and the fit (solid line). The error bars indicate the standard deviation obtained by measuring the length and concentration of at least 10 droplets.
Comparison between droplets produced in parallel at T-junctions (a)–(c) and fixed-volume droplet generators (d)–(f). Unequal flow distribution to the five junctions results in unequal sized droplets when using T-junctions, whereas the size is nearly the same when using fixed-volume droplet generators. The error bars indicate the standard deviation obtained by measuring the length of at least 10 droplets. Conditions: and (circles and micrographs), (squares), (triangles). In the case of , frequencies of generation of droplets in succeeding channels were: f = (0.46, 0.45, 0.45, 0.46, 0.46) s −1 for T-junctions, f = (0.35, 0.35, 0.37, 0.36, 0.36) s −1 for fixed-volume droplet generators; volume fractions estimated as = (0.82, 0.81, 0.85, 0.85, 0.86) for T-junctions, ϕ = (0.83, 0.86, 0.85, 0.84, 0.85) for fixed-volume droplet generators. A detailed design of the devices is provided in the supplementary material. 11
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