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Image of a device, mounted on a glass slide, fitted with capillaries and filled with liquid dye. During operation, fluid 1 (a and b) is injected as drops into immiscible stream 2. These drops are then fed by 3a and 3b into channel 4 for analysis and measurement. The constrictions in channel 4 accelerate and therefore stretch the drops. Multiple constrictions permit measurement at different interface age. The channel geometry is shown schematically in the inset, at lower right.
Freeze-frame image of drops flowing left to right in an extensional flow gradient (water drops in pdms 1000). Measurements can be done at either the entrance or exit of a constriction; the exit is shown here. When the drops leave the constriction (the channel walls appear as slanted lines in the left half of the image), the flow decelerates in proportion to the change in cross-sectional area. The drops, which are generated periodically in time, therefore, become closer together. This deceleration corresponds to a stretching in the transverse direction; note that the drops at the left side are stretched vertically, and their deformation decays as they pass to the right. Here for illustrative purposes the drops are allowed to come relatively close together (which is suboptimal for measurements, because eventually their relaxation is hindered). Generally, the drop production rate is adjusted so that there are a few drops per image.
Experimental analysis of drop deformation upon departure from the channel constriction (Taylor plot): as a function of . The radius , deformation and trajectory of the drops are measured directly by image analysis, at a rate in excess of 100 data . The slope is equal to the interfacial tension .
Summary of interfacial tension results (and fluid viscosities).a
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