Stress relaxation in a ferrofluid with clustered nanoparticles

Area of Science:

• Materials Science
• Fluid Dynamics
• Magnetohydrodynamics

Background:

• Ferrofluids exhibit unique rheological properties when subjected to magnetic fields.
• Magnetic field-induced structures, such as chains and aggregates, significantly influence ferrofluid behavior.

Purpose of the Study:

• To investigate stress relaxation in a ferrofluid composed of clustered iron nanoparticles after flow interruption under an applied magnetic field.
• To correlate residual stress with magnetic field-induced yield stress and understand the role of microstructures.

Main Methods:

• Experimental measurements of stress relaxation in a ferrofluid under magnetic field influence.
• Theoretical modeling to predict and analyze the ferrofluid's response to magnetic fields and flow interruption.

Main Results:

• Residual stress after relaxation is directly correlated with the magnetic field-induced yield stress.
• The total macroscopic stress is determined by the interplay of linear chains and dense aggregates.
• A theoretical model, despite simplifications, accurately predicts the experimentally observed behavior.

Conclusions:

• The study enhances understanding of complex magnetic field-induced rheological properties in magnetic colloids.
• The findings provide insights into ferrofluid behavior near the yield stress point, influenced by microstructural evolution.