Eur. Phys. J. E (2014) 37: 70
https://doi.org/10.1140/epje/i2014-14070-9

Regular Article

Field-dependent anisotropic microrheological and microstructural properties of dilute ferrofluids

School of Physics, University of Hyderabad, 500046, Hyderabad, India

^* e-mail: avsp@uohyd.ernet.in

Received: 28 April 2014
Revised: 12 July 2014
Accepted: 15 July 2014
Published online: 15 August 2014

Abstract

We have measured microrheological and microstructural properties of a superparamagnetic ferrofluid made of Mn_0.75Zn_0.25Fe₂O₄ (MZF) nanoparticles, using passive microrheology in a home-built inverted microscope. Thermal motion of a probe microsphere was measured for different values of an applied external magnetic field and analysed. The analysis shows anisotropy in magneto-viscous effect. Additional microrheological properties, such as storage modulus and loss modulus and their transition are also seen. We have also obtained microstructural properties such as elongational flow coefficient , relaxation time constant , coefficient of dissipative magnetization , etc., using the analysis given in Oliver Muller et al., J. Phys.: Condens. Matter 18, S2623, (2006) and Stefan Mahle et al., Phys. Rev. E 77, 016305 (2008) over our measured viscosity data. Our values for the above parameters are in agreement with earlier theoretical calculations and macro-rheological experimental measurements. These theoretical calculations consider an ideal situation of zero-shear limit, which is best approximated only in the passive microrheology technique described here and a first time measurement of all these parameters with passive microrheology.