An experimental note on the deformation and breakup of viscoelastic droplets rising in non-Newtonian fluids

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• 作者：Susana L. Ortiz ; Julia S. Lee ; Bernardo Figueroa-Espinoza ; Baltasar Mena
• 关键词：Non ; Newtonian droplets ; Viscoelastic fluids ; Critical volume ; Tail breakup ; Extensional flow ; Velocity jump ; Negative wake
• 刊名：Rheologica Acta
• 出版年：2016
• 出版时间：December 2016
• 年：2016
• 卷：55
• 期：11-12
• 页码：879-887
• 全文大小：2,520 KB
• 刊物类别：Chemistry and Materials Science
• 刊物主题：Chemistry
  Characterization and Evaluation Materials
  Polymer Sciences
  Mechanical Engineering
  Soft Matter and Complex Fluids
  Food Science
  
• 出版者：Springer Berlin / Heidelberg
• ISSN：1435-1528
• 卷排序：55

文摘

The deformation of viscoelastic droplets rising in non-Newtonian fluids is examined experimentally. Similarly to the case of bubbles and Newtonian droplets traveling in viscoelastic fluids, a critical volume exists but there is no jump in velocity nor a drastic change in droplet geometry. Nevertheless, a tail appears as well as a negative wake. For large-enough volumes, the thickness of the tail is much larger than that for the Newtonian droplets; this is also true for the magnitude of the negative wake and for the extension of the tail. The head of the droplet is subjected to a bi-axial elongation which deforms the spherical part of the droplet converting it into an elongated shape. This elongated shape blends into a tail and the droplet is converted into a viscous elongated teardrop. The tail is then subjected to a uniaxial extensional flow under the action of elongational stresses along the length of the tail. This extensional flow is counteracted by the shear stresses acting on the interface between the tail and the outer surrounding fluid. This interaction will determine the tail breakup. The influence of the elastic properties of the surrounding fluid and the extensional viscosity of the droplet will be responsible for the length and thickness of the tail as well as for its breakup mechanism.