Measurement of Static and Dynamic Magneto-Viscoelasticity in Facile Varying pH Synthesized CoFe2O4-Based Magnetic Fluid

In this work, we have investigated the size induced on the viscoelasticity of CoFe₂O₄ magnetic nanofluids (MNFs). The focus of this work is to provide an insight into the effect of varying particle size on viscoelastic properties of CoFe₂O₄ MNFs with varying CoFe₂O₄ nanoparticle sizes. Kerosene-based MNFs containing surfactant coated CoFe₂O₄ were synthesized using standard optimized coprecipitation method, and variations in average mean size ~ 9–30 nm have been synthesized. The physical properties, such as structural and morphology, have been investigated to confirm the purity, and variation in size. Steady-state and oscillatory mode measurements were performed using a magneto-rheometer to investigate the field-induced magneto-rheology. The steady-state rheograms (viscosity vs. shear rate curve) has been well fitted with power-law $\eta =c\dot {\gamma }^{n}+\eta _{\infty }$ , confirming the shear thinning behavior with $n\le 1$ . Furthermore, magneto-sweep rheograms (viscosity vs. magnetic field) has been used to investigate the steady increase in viscosity, which is due to the formation of a chain-like structure in the field direction causing an interruption in the smooth streamline flow of the MNFs. Furthermore, dynamic oscillatory measurement shows the transition between G’ and G” with applied dynamic strain confirming solid-liquid phase transition behavior. Field-induced viscoelastic behavior in static and dynamic mode provides significant information for optimization of MNFs for various applications.

I. Introduction

Viscoelastic properties of magnetic nanofluids (MNFs) play an essential role in the device development, as magnetic control on fluid behavior is a promising field in numerous applications. MNFs commonly known as ferrofluids are synthetic fluids having ultra-fine ferromagnetic and ferrimagnetic particles in the size range (2–40 nm) dispersed in the magnetically passive medium. [1] These fluids show non-Newtonian behavior when subject to the external magnetic field. Magnetic nanoparticles (MNPs) dispersed in MNFs form a chain-like structure in the field direction, which causes hindrance to the streamline fluid flow, which leads to an increase in viscosity. The morphology, dilution, carrier fluid, and surfactant of MNFs are the key parameters which strongly influence the magneto-viscous effect (MVE). Optimization of MVE with varying particle size is essential for various device applications in engineering (motors, bearings, actuators, sensors, and thermal applications), as well as biological application (hyperthermia treatment, drug delivery) [2]–[5].