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Download fileInterfacial Behavior of Particle-Laden Bubbles under Asymmetric Shear Flow
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posted on 2021-11-02, 18:06 authored by Milad Eftekhari, Karin Schwarzenberger, Sascha Heitkam, Aliyar Javadi, Aleksandr Bashkatov, Seher Ata, Kerstin EckertThe
behavior of moving bubbles has mostly been studied in an axisymmetric
flow field. To extend the knowledge to practical conditions, we investigate
the interfacial and hydrodynamic properties of bubbles under asymmetric
shear forces. Experiments are performed with a buoyant bubble at the
tip of a capillary placed in a defined shear flow in the presence
of surfactants, nanoparticles, and glass beads. The response of the
interface to the surrounding asymmetric flow is measured under successive
reduction of the surface area. Profile analysis tensiometry is utilized
to investigate the dynamic surface tension and the surface rheology
of the surfactant- and nanoparticle-laden interfaces. Microscopic
particle image and tracking velocimetry are used to study the bulk
flow and the interfacial mobility of the buoyant bubble. According
to our results, the rotational component of the shear flow provokes
an interfacial flow, which redistributes the adsorbed surfactants
and particles at the interface. In the presence of NPSCs, a contiguous
network of particles forms at the interface through densification
of surface structures. We show that this interconnected nanoparticle
network eventually stops the interfacial flow and decreases the mobility
of the glass beads at the interface. The immobilization of the interface
is characterized by a dimensionless number, defined as the ratio of
the interfacial elasticity to bulk shear forces. This number provides
an estimate of the interfacial forces required to impose interfacial
immobility at a defined flow field. Our findings can serve as a basis
to formulate boundary conditions for refined modeling and to predict
the hydrodynamics of bubbles and droplets.
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Keywords
profile analysis tensiometryasymmetric shear forcessurrounding asymmetric flowshear flow provokesaxisymmetric flow fieldasymmetric shear flowformulate boundary conditionsbulk shear forcesdynamic surface tensioninterfacial forces requiredimpose interfacial immobilitydefined shear flowdefined flow fieldmicroscopic particle imagebulk flowinterfacial flowpractical conditionssurface structuressurface rheologysurface areainterfacial elasticitytracking velocimetrysuccessive reductionrotational componentrefined modelingnumber providesladen interfaceshydrodynamic propertiesglass beadsdimensionless numbercontiguous networkcapillary placedbuoyant bubble