Paper Number
NF26 

Session
Non-Newtonian Fluid Mechanics

Title
Capillary break-up of liquid-liquid interfaces

Presentation Date and Time
October 11, 2017 (Wednesday) 11:30

Track / Room
Track 5 / Crestone B

Authors (Click on name to view author profile)

1. Formenti, Susanna (Politecnico di Milano)
2. Verbeke, Karel (KU Leuven)
3. Briatico Vangosa, Francesco (Politecnico di Milano)
4. Reddy, Naveen K. (Hasselt University)
5. Clasen, Christian (KU Leuven)

Author and Affiliation Lines (in printed abstract book)
Susanna Formenti¹, Karel Verbeke², Francesco Briatico Vangosa¹, Naveen K. Reddy³, and Christian Clasen^2
1Politecnico di Milano, Milano, Italy; ²KU Leuven, Heverlee, Belgium; ³Hasselt University, Hasselt, Belgium

Speaker / Presenter 
Formenti, Susanna

Text of Abstract
Studies of capillary breakup phenomena of liquid filaments are classically related to liquid-air interface; however, there is a variety of applications where liquid-liquid interfaces are involved. The presence of a surrounding medium of different (often similar or even higher) viscosity and an altered interfacial tension change the thinning dynamics significantly, so that classical descriptions need to be reconsidered. Pioneering studies focused mainly on the late-stage thinning and breakup dynamics close to pinch-off in dripping experiments, exploiting a large range of viscosity ratios of inner to outer fluid. For this, different similarity solutions were proposed to describe the universal pinch-off for well-defined regimes of the Navier-Stokes equations.
Here we explore the thinning behaviour away from the self-similar final stage of pinch-off for a wide range of inner and outer fluids, combining inertia controlled, viscous and intermediate fluids. To this end, the capillary thinning of filaments with Liquid-liquid interfaces is investigated, using a high-resolution optical setup together with a modified version of a capillary breakup setup. Using this novel Liquid-in-liquid technique allows to accurately control the wavelengths of the instability induced in the filament. Due to the slowed-down dynamics arising from the lower interfacial tension, capillary thinning can now be investigated in higher detail: results reveal clear transitions between different thinning regimes. In particular, we experimentally highlight a pronounced presence of the inertial-viscous regime, possibly followed by a final two-fluids viscous regime. Contrary to previous observations, the similarity prefactor, as well as the transition radii, are found to be a function of the viscosity ratio in all regimes. This dependence is compared with results from linear stability analysis considering the actual imposed wavelength.