Ethylene Glycol Based Ferrofluid for the Fabrication of Magnetically Deformable Liquid Mirrors

Stable ferrofluids composed of positively charged magnetic iron oxide nanoparticles coated with 2-[2-(2-methoxyethoxy)ethoxy]acetic acid (MOEEAA) are prepared in ethylene glycol. These new ferrofluids exhibit a magnetic response that is equivalent to that found for corresponding citrate stabilized particles. Unlike the uncoated positively charged particles, nanoparticles coated with MOEEAA and dispersed in ethylene glycol remained stable in the presence of a magnetic field. Infrared spectra indicate that surface grafting occurs through the terminal carboxylate group which is bound to the iron oxide nanoparticles both through bridging and unidentate structures. A surface grafting density of 1.2 molecules/nm² is determined from thermogravimetry measurements. Although MOEEAA functionalization increases the stability of nanoparticle suspensions in ethylene glycol, surface charge is also essential for the prevention of particle agglomeration. Importantly, the MOEEAA stabilized ferrofluid is compatible with the deposition of surface films of silver nanoparticles and thus allows for the preparation of magnetically deformable liquid mirrors.