The effect of the viscosity ratio on band formation in sheared mixtures of phase-separated polymer solutions with ultralow interface tension

Abstract

The microscopic structure and dynamics of droplet dispersions formed by phase separation of two Newtonian polymer solutions were observed under simple shear. The phases had equal volumes. Under certain conditions, these dispersions show long, wormlike, extended structures after several minutes of shearing. The development of these structures was recorded in microscopic movies. These were interpreted by calculating two-point grey value correlation functions. The divergence of the correlation in the flow direction was taken as a signature of the onset of the extended structures. It was demonstrated that a viscosity ratio far from the unity of the two phases is necessary for the formation of the long shear-stabilised structures. At a viscosity ratio close to unity, the systems maintain isolated droplets in a dynamic equilibrium of coalescence and break-up. The structure formation is the result of shear-induced coalescence. The need for a difference in viscosity between the phases suggests a relation with shear banding seen in shear-thinning systems.

GRAPHICAL ABSTRACT

Keywords:

• Shear
• interface
• band formation
• deformation, viscosity contrast

Acknowledgements

The authors would like to thank Carlo van Overbeek for contributing to this work during his stay at Forschungszentrum Jülich GmbH, Institute of Complex Systems, and Pavlik Lettinga of this institute for discussions and supervision.

Disclosure statement

No potential conflict of interest was reported by the author(s).