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Fluid Dynamics of Microgel-Covered Drops Reveal Impact on Interfacial Conditions

Fluid Process Engineering, AVT–Aachener Verfahrenstechnik, RWTH Aachen University, Forckenbeckstrasse 51; D–52074 Aachen, Germany
Institute of Physical Chemistry–IPC, RWTH Aachen University, Landoltweg 2; D–52074 Aachen, Germany
Author to whom correspondence should be addressed.
Polymers 2018, 10(8), 809;
Received: 26 June 2018 / Revised: 18 July 2018 / Accepted: 21 July 2018 / Published: 24 July 2018
(This article belongs to the Special Issue Microgels and Hydrogels at Interfaces)
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Microgels are deformable polymer-networks with conspicuous properties. Their surface- activity associated with their switchability makes their application in liquid-liquid systems, such as extraction processes, particularly promising. For their application as switchable stabilizers at the interface, a detailed understanding of their impact on process relevant phenomena, such as the sedimentation behavior, is necessary. So far, the focus of research has been on microscopic-scale properties, whereby the propagation to macroscopic effects has rarely been quantified. In this study, single microgel-covered n-butyl acetate drops rising in a quiescent continuous water phase are investigated experimentally. The dependency of the microgel properties, in terms of size and cross-linking density, on the fluid dynamics are addressed. The impact of microgels is studied in detail by sedimentation velocity, drop deformation and the resulting drag coefficient. The deformation of drops is related to shape conserving interfacial properties such as the interfacial tension. Counter to our expectations, microgel-covered drops deform less than the drops of the pure system although microgels reduce the interfacial tension. Moreover, the sedimentation velocity is of special interest, since it reveals the mobility of the interface and friction conditions at the interface. Our results demonstrate the correlation between microgel properties at the interface on a microscopic scale and the macroscopic behavior of microgel-covered drops. View Full-Text
Keywords: microgels; interfacial mobility; sedimentation; drop deformation; drag coefficient microgels; interfacial mobility; sedimentation; drop deformation; drag coefficient

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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Faulde, M.; Siemes, E.; Wöll, D.; Jupke, A. Fluid Dynamics of Microgel-Covered Drops Reveal Impact on Interfacial Conditions. Polymers 2018, 10, 809.

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