Magnetic and optical studies of magnetic colloidal particles in water and oleic acid

The macro-size magnetic colloidal particles in both distilled water and ole ic acid were prepared by using Fe3O4 ferrofluids (SMG018), the sodium dodec yl sulfate (SDS), and distilled water or oleic acid. The optical transmissi on of these ferrofluid emulsions has been investigated as functions of conc entration of SDS between 0.64 and 3.73 wt %, incident optical wavelengths b etween 450 and 750 nm, and applied magnetic fields up to 141 Oe. The optica l transmission shows maximum with concentration of SDS near 3.13 and 1.90 w t % for samples in distilled water and oleic acid, respectively. In general , under an applied magnetic field, the size of the magnetic colloidal parti cles for samples in oleic acid is smaller than that of samples in distilled water; however, the concentration of the magnetic colloidal particles is t he opposite. This can be explained due to the different aggregation ability of the magnetic colloidal particles in both distilled water and oleic acid . The optical transmission of the samples is observed to be reversed propor tional to the area covered by the magnetic colloidal particles. (C) 2000 Am erican Institute of Physics. [S0021-8979(00)91208-8].