Effect of surfactant excess in non-polar ferrofluids probed by small-angle neutron scattering

摘要

The microstructure of ferrofluids (magnetite/oleic acid/benzene) with an excess of freeoleic acid is investigated by small-angle neutron scattering (SANS). For such excess higher than 25vol. % a sharp break in the stability of ferrofluids occurs followed by coagulation and precipitation.Below this value the influence of the surfactant excess on the stability of ferrofluids is insignificant;neither particle aggregation nor surfactant agglomeration is observed. The interaction of free acidmolecules in the ferrofluids is compared with that in pure benzene solutions. A significant increasein the attraction is observed for acid molecules in the ferrofluids, which is related to the loss ofmagnetic fluids stability at high excess of acid.