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Breakup of a fluid thread in a confined geometry: droplet-plug transition, perturbation sensitivity, and kinetic stabilization with confinement

John G. Hagedorn,¹ Nicos S. Martys,² and Jack F. Douglas^3
1Mathematical and Computational Sciences Division, NIST, Gaithersburg, Maryland 20899, USA
²Materials and Construction Research Division, NIST, Gaithersburg, Maryland 20899, USA
³Polymers Division, NIST, Gaithersburg, Maryland 20899, USA
(Received 3 March 2003; published 27 May 2004)

Abstract

We investigate the influence of geometrical confinement on the breakup of long fluid threads in the absence of imposed flow using a lattice Boltzmann model. Our simulations primarily focus on the case of threads centered coaxially in a tube filled with another Newtonian fluid and subjected to both impulsive and random perturbations. We observe a significant slowing down of the rate of thread breakup ("kinetic stabilization") over a wide range of the confinement, ΛR_tube / R_thread 10 and find that the relative surface energies of the liquid components influence this effect. For Λ < 2.3, there is a transition in the late-stage morphology between spherical droplets and tube "plugs." Unstable distorted droplets ("capsules") form as transient structures for intermediate confinement (Λ ≈ 2.1−2.5). Surprisingly, the thread breakup process for more confined threads (Λ 1.9) is found to be sensitive to the nature of the initial thread perturbation. Localized impulsive perturbations ("taps") cause a "bulging" of the fluid at the wall, followed by thread breakup through the propagation of a wavelike disturbance ("end-pinch instability") initiating from the thread rupture point. Random impulses along the thread, modeling thermal fluctuations, lead to a complex breakup process involving a competition between the Raleigh and end-pinch instabilities. We also briefly compare our tube simulations to threads confined between parallel plates and to multiple interacting threads under confinement.

• Introduction
• Brief Review of the Lattice Boltzmann Model and Thread Breakup in Bulk
• Simulation Results
• Fluid thread breakup by capillary instability under weak confinement
• Confined fluid thread breakup: Localized impulsive perturbations
• Confined fluid thread breakup: Random initial perturbation
• Confined fluid thread breakup: Influence of fluid-wall interaction
• Kinetic stabilization of thread breakup and glasslike phenomenology
• Fluid thread breakup under confinement: Single and multiple threads between parallel plates
• Conclusions
• Acknowledgments
• References

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