Analytical calculation of chain length in ferrofluids

Abstract

The response of a typical ferrofluid (FF) lies in its explicit property of chain formation of magnetic nanoparticles. The most significant magneto-optic (MO) and magneto-viscous (MV) effects of FF are attributed to chaining effect. In the present research, an effort was made to analytically justify the dependence of the structure evolution of FFs on different measurable parameters involved in MO and MV effects. The problem is treated with the help of dimensional analysis and an empirical relation is formulated relating the equilibrium chain length with Verdet coefficient (constant), particle diameter, viscosity of the carrier fluid, particle density, magnetization and shear rate. The formulated relation of chain length is supported by error analysis to yield the uncertainty in the result. The maximum uncertainty in four sets of data is found as ∼0.75.

Influence of magnetic field on evaporation of a ferrofluid droplet

“…The chains formed under zero fields were attributed to the dipole-dipole interaction between the particles which compete with the thermal motion of the particles. Further it was shown that when the fluid is subjected to an external magnetic field this chain formation will be enhanced and longer chains parallel to the direction of the field will be formed [37][38][39]. Microphotographs shown in figures 2-5 also show random chains in zero fields along with random chains and enhancement of chain formation under the influence of the field.…”

Absorption spectrum of magnetically structured emulsions in the centimeter range

“…The question of the number of dispersed phase droplets in the chain structures formed in the magnetic field is rather complicated and is not posed in this study. Strictly speaking, in the athermal (non-Brownian) suspension, with which we deal in this study, there are no obvious mechanisms for limiting the growth of chain structures in the applied field [41,42], in contrast to diffusion-limited growth in thermal (Brownian) suspensions [43][44][45]. To be able to still perform some calculations we will vary the number of droplets in the chain, assuming that varying the magnitude of the field produces a similar effect, leading to a change in the length of the chain structures.…”