Capillary viscosimetry on ferrofluids

Abstract

Experiments performed for different ferrofluids under shear flow have shown that an increase of the magnetic field strength applied to the sample yields an increase of the fluid's viscosity, the so called magnetoviscous effect. It has been shown that the magnitude of the effect is strongly related to the modification of the microstructure of ferrofluids and can be influenced by varying both the dipole-dipole interaction between the particles and the concentration of large particles within the fluid. This result has been further used to synthesize new ferrofluids which, on one hand, are more compatible for technical applications but, on the other hand, led to difficulties for the experimenters in measuring the viscous behavior in the presence of a magnetic field. To overcome this problem, a specially designed ferrofluid-compatible capillary viscometer has been developed. Within this paper, the experimental setup as well as experimental results concerning the investigation of the magnetoviscous effect in both diluted and concentrated cobalt-based ferrofluids are presented.

Controlling lateral nanomixing and velocity profile of dilute ferrofluid capillary flows in uniform stationary, oscillating and rotating magnetic fields

“…Inflation of apparent viscosity in capillaries, i.e., rotational viscosity, is a well-known consequence of such MNP hindrance [2]. Although there have been numerous studies on laminar and turbulent flow of ferrofluids under a coaxial SMF [10,[42][43][44][45][46][47][48][49], the transport properties of low-Re capillary flows has not received enough attention to date. Thus, we performed Taylor dispersion tests in capillaries to clarify in which manner interactions under SMF between excited MNPs and laminar flow fields may influence lateral mass transfer.…”

Anisotropy of the magnetoviscous effect in a cobalt ferrofluid with strong interparticle interaction

“…The fluid was supplied by the Strem Chemicals GmbH similar to the samples Co87-02 and Co87-03 studied in [15,16]. It contained cobalt nanoparticles coated with an aluminum oxide shell, stabilized with KorantinSH (N-oleyl sarcosine) [6], suspended in kerosene.…”

“…A field-induced change in the viscosity of a magnetic fluid was first observed in 1969 by McTague for a cobalt ferrofluid [14] and has since been studied experimentally [15][16][17][18][19][20] and theoretically by several groups [21][22][23][24][25][26][27][28]. The increase in the viscosity is a function of the direction of the applied magnetic field with respect to the direction of the fluid flow and the vorticity [14,21].…”

“…The increase in the viscosity is a function of the direction of the applied magnetic field with respect to the direction of the fluid flow and the vorticity [14,21]. However, most studies of the magnetoviscous effect have been performed using rotational or capillary flow viscometers [15][16][17][18], in which only one of the Miesowicz viscosity coefficients [29] is experimentally accessible due to the rotational symmetry of the measuring system. Hence little or no information regarding the anisotropy of the MVE has been gained.…”

A capillary viscometer designed for the characterization of biocompatible ferrofluids

“…While the principle of a capillary viscometer has already been used to measure the MVE of magnetic fluids [26,27] the shear rate ranges of the new setup as well as the magnetic field strength applied is adapted to ranges proved to be relevant in a potential biomedical application.…”