Testing the mean magnetization approximation, dimensionless and scaling numbers in magnetorheology

Area of Science:

• Magnetorheology
• Soft Matter Physics
• Materials Science

Background:

• The mean magnetization (MM) approximation simplifies particle behavior in magnetorheological fluids.
• This approximation treats particles as effective dipole moments, crucial for theoretical and simulation studies.
• Mathematical justification for the MM approximation's widespread use is often lacking.

Purpose of the Study:

• To rigorously test the validity of the mean magnetization approximation.
• To evaluate the approximation's applicability across diverse magnetic field strengths and particle concentrations.
• To compare the MM approximation's performance in conventional magnetorheological fluids (CMRFs) and inverse ferrofluids (IFFs).

Main Methods:

• Experimental investigations
• Theoretical analysis
• Computational simulations

Main Results:

• The MM approximation is found to be highly applicable in IFFs up to 265 kA m⁻¹ field strengths and 20 vol% particle loadings.
• For CMRFs, the MM approximation is valid only under conditions of magnetic saturation.
• In CMRFs, the approximation is also applicable in the limit of infinite dilution.

Conclusions:

• The MM approximation offers a reliable framework for IFFs within tested parameters.
• The MM approximation's utility in CMRFs is significantly constrained, requiring specific conditions for accuracy.
• This study clarifies the scope and limitations of the MM approximation in magnetorheology.