Study on Influence Law and Mechanism of Rheological Properties of High-Viscosity Fluoroether Oil-Based Ferrofluids

A series of high-viscosity ferrofluids with variations in particle concentration and carrier liquid molecular weight were synthesized in a fluoroether oil base by the chemical coprecipitation method. The microstructure, surface coating, and magnetic properties of the nanoparticles were characterized, and the rheological properties of the corresponding ferrofluids were systematically investigated to elucidate their governing mechanisms and underlying mechanisms. The results indicate that the synthesized zinc-doped ferrite particles are spherical with a size of less than 50 nm and are chemically coated with a fluoroether acid. Moreover, the saturation magnetization of the ferrofluids increases with rising particle concentration. With the increase in particle concentration, the zero-field viscosity and shear stress of the ferrofluids increase significantly. The zero-field viscosity and shear yield stress of the ferrofluid increase significantly with the molecular weight of the carrier liquid, due to the strengthened entanglement of its molecular chains. At a carrier liquid molecular weight of 4600 g/mol, the 50 wt.% ferrofluid displayed a liquid character, in contrast to the gel-like character displayed by the 60 and 70 wt.% samples. The 60 wt.%-7480 g/mol sample demonstrated superior elasticity to its 60 wt.%-4600 g/mol counterpart. Furthermore, the application of a 100 mT magnetic field induced a transition from a liquid to a gel state in the 50 wt.%-4600 g/mol sample. This transition, driven by the formation of magnetic field-induced chain-like structures, significantly enhanced the magnetoviscous effect. This study provides the theoretical basis and experimental support for the development of high-viscosity ferrofluid sealing materials suitable for high-pressure, liquid environments and corrosive working conditions.