Study Of Synthesis And Properties For The Preparation Of Oleic Acid Coated ?-Fe₂O₃ Nanoparticles By Chemically Induced Method And Kerosene-based Ferrofluids

Exploring new synthetic methods and new application fields are still the mainstream direction of micro-nano materials research.As a magnetically controllable functional material,magnetic materials have more practical application prospects than other materials.Using a chemically induced transition method,magnetic nanoparticles of?-Fe₂O₃ coated by oleic acid??-Fe₂O₃@oleic acid nanoparticles?can be prepared by adding the oleic acid during the synthesis or post-synthesis.The magnetization,morphology,atom ration,crystal structure were characterized by vibrating sample magnetometer?VSM??transmission electron microscope?TEM??x-ray dispersive spectroscopy?EDS??x-ray diffraction?XRD?.The modified nanoparticles have been used to synthesize a high-quality kerosene-based ferrofluids by heating and stirring dispersion method,studying their magnetization properties and magneto-optical effect.The characterization of the modified nanoparticles show that the particles are approximately spherical;the particles of no oleic acid modification are still composed of?-Fe₂O₃ core and FeCl₃?6H₂O shell;the amount of oleic acid added is sufficient,the FeCl₃?6H₂O shell can be replaced by oleic acid,with the as-prepared sample single?-Fe₂O₃@oleic acid nanoparticles,whereas the as-prepared sample is a mixture of both?-Fe₂O₃@FeCl₃?6H₂O and?-Fe₂O₃@oleic acid nanoparticles;the specific saturation magnetization values of the particles are 70 A?m²/kg?emu/g?.The characterization of ferrofluids shows that quality of the com-particles??-Fe₂O₃@oleic acid nanoparticles?modified by oleic acid for post-synthesis was better than during the synthesis;a uniformly stable ferrofluids is obtained by aging treatment and centrifugation,the mass fraction??_m?and volume fraction??_v?of the ferrofluids can be calculated by measuring the density;the magnetization curves of the particles and ferrofluids were measured by VSM,and compared with the particles magnetization curves and the ferrofluids reduction magnetization curves to evaluate the quality of the magnetic fluid.Optical transparency measurements confirmed that the ferrofluids showed a sensitive field-induced effect of chain-like aggregation,with redispersion of the particles after removing the magnetic field.So the study of field-induced effect of light transmission can further characterize the quality of ferrofluids.The field-induced optical effect theory was measured using circularly polarized light,and the linear optical effect?magnetic birefringence and magnetic dichroism?of the ferroliquids under a uniform magnetic field was studied using the?-scan technique.Studies have shown that circularly polarized light travels through an anisotropic medium,birefringence and dichroism effects cause the transmitted light to behave as elliptically polarized light.Using angular scan by a continuously rotating polarizer as analyzer,the angular???distribution curve of relative intensity?T?corresponding to elliptically polarized light can be measured.From the T-?curve having ellipsometry,the parameters such as the ratio of short to long axis,and angular orientation of the long axis to the vertical field direction can be obtained.Thus,magnetic birefringence??n?and dichroism????can be probed simultaneously by measuring magneto-optical,positive or negative birefringence and dichroism features from the transmission mode.The proposed method is called?-scan technique,and can accurately determine sample stability,magnetic field direction,and cancel intrinsic light source ellipticity.This study may be helpful to further research done to ferrofluids and other similar colloidal samples with anisotropic optics.