Abstract
The rising of a Newtonian oil drop in a non-Newtonian viscous solution is studied experimentally. In this case, the shape of the ascending drop is strongly affected by the viscoelastic and shear-thinning properties of the surrounding liquid. We found that the so-called velocity discontinuity phenomena is observed for drops larger than a certain critical size. Beyond the critical velocity, the formation of a long tail is observed, from which small droplets are continuously emitted. We determined that the fragmentation of the tail results mainly from the effect of capillary effects. We explore the idea of using this configuration as a new encapsulation technique, where the size and frequency of droplets are directly related to the volume of the main rising drop, for the particular pair of fluids used. These experimental results could lead to other investigations, which could help to predict the droplet formation process by tuning the two fluids’ properties, and adjusting only the volume of the main drop.
Highlights
The problem of encapsulating droplets of fluid has important implications in the fields of bioengineering and medical research, for instance to encapsulate cells [1]
We explore the idea of using this configuration as a new encapsulation technique, where the size and frequency of droplets are directly related to the volume of the main rising drop, for the particular pair of fluids used
We investigated the instability occurring at the tail of a Newtonian drop rising in a viscoelastic fluid
Summary
The problem of encapsulating droplets of fluid has important implications in the fields of bioengineering and medical research, for instance to encapsulate cells [1]. Some studies have addressed the case of a Newtonian jet flowing from a nozzle in a viscoelastic fluid [28,29,30] In those experiments, the jet fragmenting is controlled by the injection flow, while, in the present case, the filament is created directly by the rising drop. We discuss different aspects of the droplets formation, by relating the velocity and volume of the main drop, the size of the tail appearing behind the drop and the size and frequency of formation of the droplets These results, obtained only for a single pair of Newtonian/non-Newtonian fluids, could lead to a more extensive investigation with which this phenomenon could be fully understood
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