FTIR study of surfactant bonding to FePt nanoparticles

FePt nanoparticles coated with 2 nm thick films of surfactant have been studied as candidates for magnetic recording media. The self-assembly of these nanoparticles is influenced by the properties of their surfaces which are coated with a layer of mixed oleic acid and oleyl amine. These surfactant coated FePt nanoparticles were characterized using Fourier transform infrared spectroscopy (FTIR). The observation of both ν(COO) and ν(C=O) vibrational modes indicates that oleic acid bonds to the FePt nanoparticles in both monodentate and bidentate forms. The oleylamine bonds to the FePt nanoparticles through electron donation from the nitrogen atom of the NH2 group. The FTIR spectra indicate that there is a conversion of the alkyl chains from the oleyl form (cis-9-octadecenyl) to the elaidyl form (trans-9-octadecenyl) during the synthesis of the FePt nanoparticles. This is revealed by the presence of several vibrational absorption bands in the region of the olefinic C-H stretching modes. The presence of elaidyl groups on the FePt surfaces is very important because the structures of the oleyl groups and the elaidyl groups are quite different and are expected to pack differently around the FePt nanoparticles. This in turn will influence the self-assembly of nanoparticles on substrates