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Published on: April 10, 2017
Detachment forces during parallel-plate gap separation mediated by a simple yield-stress fluid.
Vítor Hugo de Oliveira Pereira1, Wilson Barros2
1Departamento de Física, Universidade Federal de Pernambuco (UFPE), Cidade Universitária, 50670-901, Recife, Pernambuco, Brazil.
This study reveals how yield-stress fluids behave under traction, showing instability at small gaps and stable flow at larger ones. We isolated viscosity, capillarity, and yield stress contributions to traction force.
Area of Science:
- Fluid mechanics
- Rheology
- Soft matter physics
Background:
- Yield-stress fluids exhibit complex flow behaviors.
- Understanding traction forces is crucial for industrial applications.
Purpose of the Study:
- To monitor and analyze the normal traction force response of yield-stress fluids.
- To investigate the influence of confinement geometry and initial gap on fluid behavior.
- To differentiate and quantify contributions of viscosity, capillarity, and yield stress to traction force.
Main Methods:
- Experimental setup involving two circular parallel plates separated at constant velocity.
- Visual inspection for Saffman-Taylor instability and fingering patterns.
- Application of the Herschel-Bulkley model to analyze traction force scaling.
Main Results:
- Saffman-Taylor instability observed at narrow initial gaps, characterized by fingering patterns.
- Stable circular symmetry maintained at larger initial gaps, indicating absence of instability.
- Cascade of traction force contributions allowed isolation of viscosity, capillarity, and yield stress effects.
Conclusions:
- The study successfully isolated and quantified individual force contributions in yield-stress fluids.
- Instability is a key factor influencing fluid behavior and traction forces at small scales.
- The Herschel-Bulkley model effectively describes traction force scaling across different regimes.

