Effect of temperature on steady shear magnetorheology of CoNi microcluster-based MR fluids

• Temperature-dependent steady shear magnetorheological studies of Co-rich CoNi containing magnetic fluids are performed.
• Significant temperature-induced thinning effect of magnetorheological parameters reported.
• Quantitative estimation of temperature sensitive parameters i.e. yield stress, saturation magnetization and carrier fluid viscosity are shown using empirical methods.
• A time-temperature-field superposition method is used to construct master curves for samples with different volume fractions of particles.
• A satisfactory collapse of rheograms at different temperatures and magnetic fields implies that the systems are dynamically identical under the varying conditions.

We present the study of magnetorheological properties of magnetic fluids containing Co-rich CoNi microcluster that have been measured as a function of both magnetic field and temperature. Co-rich microclusters were synthesized by conventional homogeneous nucleation in liquid polyol. Morphological characterization using FESEM revealed the average diameter of microclusters as 450 nm. Crystal structure and room temperature magnetization measurements were performed by powder XRD and vibrating sample magnetometry. Two MR samples of different particle volume fractions were prepared. Temperature-dependent steady shear MR characterizations for both the samples in the range of 25–55 °C demonstrated systematic decline of MR parameters with increasing temperatures. The temperature-induced thinning of shear stress and viscosity was explained in terms of change in effective volume fraction. To analyze the measured variation in MR response with increasing temperature, suitable temperature-sensitive scaling parameters were also constructed. Finally to generalize the trend, rheological master curves were constructed by using time-temperature-field superposition method.