Preparation and characterization of a new magnetic fluid with good low temperature resistance

Magnetic fluids are a type of novel functional material that has emerged over the past two decades, which have found applications in various aspects of production and daily life. However, the application of conventional magnetic fluids in low-temperature environments is severely limited and often unsatisfactory. To address this issue, we have developed a new magnetic fluid with excellent low-temperature resistance. Initially, bare Fe₃O₄ magnetic nanoparticles (FMNPs) were synthesized via co-precipitation without a protective gas. Subsequently, these particles were modified using polyethylene glycol (PEG)-4000 as a surfactant. The bare and modified FMNPs (MFMNPs) were characterized using X-ray diffraction (XRD), vibrating sample magnetometer (VSM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis-differential thermal gravimetric (TGA-DTG) analysis. The rheological properties, low-temperature resistance of the magnetic fluid were also evaluated. The characterization results indicate that the MFMNPs are spherical and monodisperse, with a narrow size distribution and a mean particle size of approximately 12 nm. Furthermore, the FTIR spectra and TGA-DTA results suggest that PEG-4000 is linked to the bare Fe₃O₄ particles via hydrogen bonding, indicating successful modification of the Fe₃O₄ magnetic nanoparticles using PEG. VSM measurements demonstrate that surface modification does not alter the crystal morphology or superparamagnetic of Fe₃O₄. However, it does reduce the saturation magnetization from 68.17 to 54.75 emu/g. Additionally, the prepared magnetic fluid exhibits shear thinning and magnetic viscosity effects. It also exhibits excellent low-temperature resistance, maintaining good fluidity without freezing even at –60 °C. In summary, these results collectively indicate that the new low-temperature resistant magnetic fluid developed in this study is stable and has broad application prospects.