Raman spectroscopy in magnetic fluids

In this work Raman spectroscopy was used to investigate uncoated magnetic fluids (UMF's) and coated magnetic fluids (CMF's). The coating agents were N-oleoylsarcosine, dodecanoic acid, and ethoxylated polyalcohol. The Raman probe is the hydroxyl (OH) group chemisorbed at the magnetic nanoparticle surface and the measurements were performed in the typical OH bending and OH stretching regions. The room temperature Raman data obtained from the UMF's and CMF's are compared to each other and with the data obtained from liquid water. Suppression of Raman modes from the MF's are discussed in terms of symmetry reduction and in terms of the interaction between the chemisorbed OH-group and the surrounding medium. The relative grafting coefficient associated to different coatings are estimated from the Raman data. The highest grafting coefficient is achieved with a single coating of dodecanoic acid in the hydrocarbon-based MF. The surface-grafting coefficient of the N-oleoylsarcosine-coated MF reduces when the polar liquid carrier replaces the non-polar liquid carrier. In comparison to liquid water, it was found that the hydrogen bonding between the chemisorbed OH-group and the solvent was enhanced in UMF's and reduced in CMF's.