Behavior of nanoparticle clouds around a magnetized microsphere under magnetic and flow fields

Area of Science:

• Colloid and Surface Science
• Magnetohydrodynamics
• Biophysics

Background:

• Bimodal magnetic suspensions exhibit colloidal stabilization and efficient magnetic separation.
• Nanoparticle clouds form around microparticles in magnetic fields, influencing suspension properties.

Purpose of the Study:

• Investigate the size and shape of nanoparticle clouds under combined magnetic field and flow.
• Understand the interplay between hydrodynamic and magnetic forces on nanoparticle cloud dynamics.

Main Methods:

• Experimental observation of iron oxide nanocluster clouds around nickel microspheres in a slit channel.
• Microscopic visualization of nanocluster cloud behavior under varying flow speeds and magnetic field orientations.
• Development of a theoretical model balancing stresses and particle fluxes.

Main Results:

• Cloud size decreases monotonically with increasing flow speed in both longitudinal and transverse magnetic fields.
• Flow induces asymmetry in nanoparticle clouds in a longitudinal magnetic field.
• A simple model accurately predicts flow effects on cloud size and shape, governed by the Mason number.

Conclusions:

• Hydrodynamic forces play a significant role in reducing nanoparticle cloud size with increasing flow.
• The Mason number is the key dimensionless parameter determining cloud size under strong magnetic interactions.
• Brownian motion appears negligible in influencing cloud behavior at high magnetic interaction strengths.