Dynamic magnetic birefringence in a viscoelastic ferrocolloid

Abstract

A model is developed to describe the oscillations of optical anisotropy induced in a viscoelastic ferrocolloid (nanodispersion of magnetic particles) by an AC magnetic field. The viscoelasticity of the matrix (carrier medium) is assumed to obey the Jeffreys rheological scheme, whose advantage is that with the aid of just two viscous parameters and a single one for elasticity it enables one to vary the retarded mechanical response of the carrier from a weakly Maxwellian fluid to a medium with the rheology of a Kelvin gel. As the orientational motion of the particles driven by the AC field is always strongly affected by thermal motion, the occurring process is described with the aid of a kinetic (Fokker–Planck type) equation that combines diffusional and drift terms. On this basis, an exact evolution equation for the macroscopic optical anisotropy of a ferrocolloid is derived that is, however, just one link in an infinite chain of equations for statistical moments. The solution is obtained by applying effective field approximation: reducing the number of moment equations to their minimum and closing the chosen set. This solution is substituted to the scheme of a standard polarimetric set-up, and it is demonstrated how the peculiarities imparted by viscoelasticity should manifest themselves on the intensity of the light transmitted through the set up containing a ferrocolloid sample. This article is part of the theme issue ‘Transport phenomena in complex systems (part 2)’.

Transport phenomena in complex systems (part 2)

“…These studies are continued in the papers [37][38][39][40], where multiscale modelling of such phenomena based on the phase-field, phase-field crystal, molecular dynamics and cellular automata methods has been carried out. The effects of external processes such as magnetic fields and hydrodynamic flows on transport peculiarities have been analysed in [19,[41][42][43]. In addition, applications of nonlinear haemodynamics to myocardial revascularization are studied in [19] with special attention to the influence of bifurcation lesions in coronary arteries.…”