Effect of Surfactant Excess in Non-Polar Ferrofluids Probed by Small-Angle Neutron Scattering
The microstructure of ferrofluids (magnetite/oleic acid/benzene) with an excess of free oleic acid is investigated by small-angle neutron scattering (SANS). For such excess higher than 25 vol. % 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 acid molecules in the ferrofluids is compared with that in pure benzene solutions. A significant increase in the attraction is observed for acid molecules in the ferrofluids, which is related to the loss of magnetic fluids stability at high excess of acid.
V.I. Petrenko et al., "Effect of Surfactant Excess in Non-Polar Ferrofluids Probed by Small-Angle Neutron Scattering", Solid State Phenomena, Vols. 152-153, pp. 198-201, 2009