Effective interfacial tension in flow-focusing of colloidal dispersions: 3D numerical simulations and experiments

Abstract

An interface between two miscible fluids is transient, existing as a non-equilibrium state before complete molecular mixing is reached. However, during the existence of such an interface, which typically be at short timescales, composition gradients at the boundary between the two liquids cause stresses effectively mimicking an interfacial tension. Here, we combine numerical modelling and experiments to study the influence of an effective interfacial tension between a colloidal fibre dispersion and its own solvent on the flow in a microfluidic system. In a flow-focusing channel, the dispersion is injected as core flow that is hydrodynamically focused by its solvent as sheath flows. This leads to the formation of a long fluid thread, which is characterised in 3D using Optical Coherence Tomography and simulated using a volume of fluid method. The simulated flow and thread geometries very closely reproduce the experimental results in terms of thread topology and velocity flow fields. By varying the effective interfacial tension numerically, we show that it clearly influences threading dynamics and that it can be described by an effective capillary number. Furthermore, we demonstrate that the applied methodology provide means to measure the ultra-low but dynamically highly significant effective interfacial tension.

arXiv comment23 pages, 14 figures, under consideration for publication in Journal of Fluid Mechanics

References in corpus (4)

• A Computational Method for Sharp Interface Advection
• Volume-of-fluid simulations in microfluidic T-junction devices: Influence of viscosity ratio on droplet size
• Off-equilibrium surface tension in colloidal suspensions
• Three dimensional simulations of viscous folding in diverging microchannels

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• A Locally Corrected Multiblob Method with Hydrodynamically Matched Grids for the Stokes Mobility Problem
• Formation of colloidal threads in geometrically varying flow-focusing channels
• Local slip length and surfactant effects on liquid-infused surfaces