Discontinuous shear thickening in concentrated suspensions

Area of Science:

• Rheology of concentrated suspensions
• Soft matter physics
• Material science

Background:

• Concentrated suspensions can exhibit jamming transitions, where particle-network formation blocks flow above critical stress.
• Discontinuous shear thickening (DST) in suspensions is a key phenomenon studied in soft matter physics.
• Understanding jamming is crucial for controlling the flow properties of complex fluids.

Purpose of the Study:

• To investigate the jamming transition in magnetic particle suspensions with discontinuous shear thickening.
• To evaluate existing models for shear thickening against experimental observations.
• To explore the influence of magnetic fields and extrusion on the jamming dynamics.

Main Methods:

• Rheological measurements under controlled stress and shear rate.
• Analysis of stick-slip behavior in shear rate.
• Extrusion experiments through a die.
• Application of external magnetic fields.

Main Results:

• A standard viscosity divergence model poorly describes the observed jamming in these suspensions.
• Stick-slip behavior in shear rate was observed above the critical stress, with a period dependent on frictional contact relaxation time.
• Magnetic fields reduced the critical shear rate but did not contribute to the yield stress of the jamming transition.
• Jamming transition dynamics during extrusion were significantly slower than in rotational rheometry.

Conclusions:

• The jamming transition in these magnetic suspensions is complex and not fully captured by simple viscosity divergence models.
• Frictional contact dynamics play a critical role in the observed stick-slip flow.
• External fields like magnetism can modulate jamming, but their contribution to the yield stress is distinct.
• Flow geometry significantly impacts the dynamics of jamming transitions in concentrated suspensions.