Perturbational Statistical Theories of Magnetic Fluids

Abstract

The theories that account for the colloidal structure of a magnetic fluid give far better results than the gas-type or mean-field models. We show this by using standard perturbative approaches of colloidal science and expressing the magnetization M(H) and the initial magnetic susceptibility χ as Taylor series about the Langevin values M L (H) and L χ . One of the methods surveyed enables the structural study of the ferrocolloid through the analysis of the pair distribution function. We give a polar plot of this object when an external magnetic field H is present, showing the effect it has on the otherwise isotropic suspension.

Theory and simulation of anisotropic pair correlations in ferrofluids in magnetic fields

“…For zero field (α = 0), substituting L 3 (0) = 0 in to Eq. (18) confirms that β 02 (x) = γ 02 (x)/3 coincides with the isotropic function derived in Ref. 35 and listed in Table I.…”

“…10 Field-induced anisotropies in particle correlations have been examined previously by scattering experiments, [11][12][13][14][15] theory, 14,[16][17][18][19][20] and computer simulation. [20][21][22][23] There are, of course, existing theories for the structures of ferrofluids.…”

The influence of long range interparticle correlations on the magnetically induced optical anisotropy in magnetic colloids

“…The influence of the long range interparticle correlation on the magnetically induced dichroism and birefringence in magnetic colloids was theoretically described in Refs. [9,10] respectively. These two classes of models, based on particle agglomeration and long range interparticle correlation, predict the possibility of magnetically induced optical anisotropy in magnetic colloids made of spherical particles as well as a nonlinear dependence of dichroism and birefringence on the particle concentration.…”

“…Using the pair correlation function in a colloidal suspension of magnetic nanoparticles developed by Ivanov and Kuznetsova [11], Popescu and Socoliuc [9] derived the magnetic colloid absorption coefficient for light polarized parallel and perpendicular to the magnetic field, which allowed for the description of the magnetically induced linear dichroism dependence on magnetic particle size and concentration. It was found that the dichroism has a nonlinear dependence on the magnetic particle concentration.…”

“…[9], which was limited to parallel and perpendicular polarization states of the light as well as to the unrealistic hypothesis of neglecting the nonmagnetic and the surfactant layers at the surface of the coloidal magnetic nanoparticles, to the influence of the magnetic field on the complex refractive index of magnetic colloids for light polarized to an arbitrary angle with respect to the external magnetic field direction and also make the model explicitly dependent on the thickness of the surfactant layer. Numerical evaluations of the model are presented in order to investigate the influence of the magnetic field intensity, particle diameter and concentration, surfactant layer thickness and light polarization angle on the absorption coefficient of concentrated magnetic colloids made of spherical particles.…”