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Detachment forces during parallel-plate gap separation mediated by a simple yield-stress fluid.

The European physical journal. E, Soft matter·2024
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Delaying viscous fingering patterns during fluid detachment.

Vítor Hugo de Oliveira Pereira1, Wilson Barros1

  • 1Departamento de Física, Universidade Federal de Pernambuco (UFPE), Cidade Universitária, Recife, Pernambuco, 50670-901, Brazil. wilson.barrosjr@ufpe.br.

Soft Matter
|January 5, 2026
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Summary
This summary is machine-generated.

Researchers developed a method to prevent viscous fingering instability during thin-film detachment by adding an external fluid cap. This technique delays instability growth, reducing or eliminating fingering patterns for uniform sample distribution.

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Area of Science:

  • Rheology and Fluid Dynamics
  • Materials Science
  • Surface Physics

Background:

  • Viscous fingering instability commonly occurs during thin-film detachment.
  • This instability arises from high-velocity flow fields near plate boundaries.
  • Such patterns negatively impact uniform sample distribution in applications.

Purpose of the Study:

  • To investigate a novel method for delaying or eliminating viscous fingering instability.
  • To explore the effect of an external fluid cap on interface stability during detachment.
  • To determine the optimal conditions for instability suppression and its impact on traction forces.

Main Methods:

  • Experimental investigation using a rheometer in probe-tack mode with a yield stress fluid.
  • Systematic variation of initial gap, detachment velocity, and external fluid cap volume.
  • Monitoring normal force versus gap separation and in-situ video recording of the detachment process.

Main Results:

  • An external fluid cap effectively moves the air-fluid interface away from high-velocity zones.
  • This repositioning delays instability growth, reducing or completely removing fingering patterns.
  • Complete removal of fingering was achieved without affecting the peak normal traction force, though an additional leveled-off force interval was observed.

Conclusions:

  • The external fluid cap method is a robust approach to control viscous fingering.
  • This technique offers an alternative for achieving uniform sample distribution in fluid-surface contact applications.
  • The method successfully delays and can eliminate detrimental fingering effects.