scholarly journals Transport Coefficients and Orientational Distributions of Rodlike Particles with Magnetic Moment Normal to the Particle Axis under Circumstances of a Simple Shear Flow

2005 ◽  
Vol 71 (708) ◽  
pp. 2038-2046 ◽  
Author(s):  
Akira SATOH ◽  
Masataka OZAKI ◽  
Teppei ISHIKAWA ◽  
Tamotsu MAJIMA
Keyword(s):  
Shear Flow ◽  
Simple Shear ◽  
Magnetic Moment ◽  
Transport Coefficients ◽  
Simple Shear Flow ◽  
Rodlike Particles

Transport Coefficients and Orientational Distributions of a Dilute Colloidal Dispersion Composed of Hematite Particles: Analysis for an Applied Magnetic Field Parallel to the Angular Velocity Vector of Simple Shear Flow

2006 ◽  
Author(s):  
Ryo Hayasaka ◽  
Akira Satoh ◽  
Tamotsu Majima
Keyword(s):  
Magnetic Field ◽  
Shear Flow ◽  
Magnetic Moment ◽  
Flow Direction ◽  
Transport Coefficients ◽  
Colloidal Dispersion ◽  
Field Direction ◽  
Simple Shear Flow ◽  
Magnetic Field Direction ◽  
The Magnetic Field

We have studied the influences of the magnetic field, shear rate, and random forces on transport coefficients such as viscosity and diffusion coefficient, and also on the orientational distributions of hematite particles composed of a dilute colloidal dispersion. Hematite particles are modeled as spheroids with a magnetic moment normal to the particle axis. In the present analysis, these particles are assumed to conduct the rotational Brownian motion in a simple shear flow as well as an external magnetic field. The basic equation of the orientational distribution function has been derived from the balance of the torques and solved by the numerical analysis method. The results obtained here are summarized as follows. With increasing the magnetic field, since the magnetic moment is strongly restricted to the magnetic field direction, the motion of the particle is forced to rotate in directions normal to the shear flow direction. In the case of a strong magnetic field and a smaller shear rate, the rodlike particles can freely rotate in the xy-plane with the magnetic moment remaining pointing to the magnetic field direction. On the other hand, for a strong shear flow, the particle has a tendency to incline in the flow direction with the magnetic moment pointing to the magnetic field direction. Additionaly, the diffusion coefficient gives rise to smaller values than expected, since the rodlike particle sediments with the particle inclining toward directions normal to the moment direction.

Negative Viscosity Due to Magnetic Properties of a Semi-Dense Colloidal Dispersion Composed of Ferromagnetic Rod-Like Particles With Magnetic Moment Normal to the Particle Axis

2007 ◽  
Author(s):  
Yasuhiro Sakuda ◽  
Akira Satoh
Keyword(s):  
Magnetic Field ◽  
Shear Flow ◽  
Simple Shear ◽  
Magnetic Moment ◽  
Flow Direction ◽  
Colloidal Dispersion ◽  
Magnetic Interactions ◽  
Simple Shear Flow ◽  
Magnetic Field Direction ◽  
Negative Viscosity

We have investigated the negative viscosity of a colloidal dispersion composed of ferromagnetic rod-like particles, which have a magnetic moment normal to the particle axis. A simple shear flow problem has been treated to clarify the particle orientational distribution and rheological properties of such a semi-dense dispersion, under circumstances of an external magnetic field applied in the direction normal to the shear plane of a simple shear flow. The results obtained here are summarized as follows. For the cases of a very strong magnetic field and magnetic interactions between particles, the magnetic moment of the rodlike particles is significantly restricted in the magnetic field direction, so that the particle approximately aligns in the shear flow direction. Also, the particle can easily rotate around the axis of the cluster almost freely even in a simple shear flow. Characteristic orientational properties of the particle cause negative viscosity, as in the previous study for a dilute dispersion. However, magnetic particle-particle interactions have a function to make such negative viscosity decrease.

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