Lateral migration of viscoelastic droplets in a viscoelastic confined flow: role of discrete phase viscoelasticity

• Published in: Soft matter Vol. 15; no. 44; pp. 93 - 91
• Main Authors: Hazra, Shamik, Mitra, Sushanta K, Sen, Ashis Kumar
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 2019
• Subjects: Computational fluid dynamics; Confined flow; Droplets; Elasticity; Empirical analysis; Laminar flow; Rheometry; Viscoelastic fluids; Viscoelasticity; Viscosity; Viscosity ratio
• ISSN: 1744-683X; 1744-6848
• DOI: 10.1039/c9sm01469a

The cross-stream motion of viscoelastic droplets in viscoelastic fluids has received little attention since the classical study of migration of drops in a second order fluid. In this work, going beyond the existing classical theory, we experimentally elucidate the effect of drop-to-medium viscosity ratio k and elasticity ratio ξ on wall and center migration of viscoelastic droplets in a Poiseuille flow of a viscoelastic medium (PVP) at low Reynolds numbers (Re < 1). We observed a contrasting migration behavior of Newtonian and viscoelastic droplets having the same viscosity ratios and propose the presence of a lift force F VD due to the viscoelasticity of the droplet phase. We use analytical scaling and empirical modelling to show that the force F VD scales with a prefactor that depends upon the Weissenberg number Wi D and drop-to-medium viscosity ratio k and elasticity ratio ξ . Further, we utilize the proposed force for sorting of viscoelastic and Newtonian droplets. We study wall and center migration of viscoelastic droplets in a Poiseuille flow of viscoelastic medium (PVP) at low Reynolds numbers (Re < 1) and propose the existence of a new lift force whose origin lies in the viscoelasticity of the droplet phase.