Ferromagnetic ferrofluids in aqueous and low-polar media.

Currently known ferromagnetic ferrofluids (FFs), or liquid magnets, are typically composed of permanently magnetic barium hexaferrite nanoplatelets (BHF NPLs) dispersed in 1-butanol, where colloidal stability is achieved through electrostatic repulsion. Here, we report the development of an environmentally friendly, water-based ferromagnetic ferrofluid, in which magnetic dipolar attractions are effectively suppressed by a synergistic combination of electrostatic, steric, and hydration repulsion. We further demonstrate that stable ferromagnetic ferrofluids can also be realized in low-polarity organic solvents such as dichloromethane (DCM) and 1-hexanol, relying solely on sufficient steric-solvation repulsion-without the need for long-range electrostatic repulsion. These different types of ferromagnetic FFs offer a promising platform for tubeless microfluidic pumping in diverse chemical systems.