Interaction of Fatty Acid Monolayers with Cobalt Nanoparticles

Stable colloidal suspension of magnetic nanoparticles is challenging owing to both van der Waals forces and magnetic dipolar interactions. Thus, it is essential to coat magnetic nanoparticles with a surfactant during chemical synthesis in order to prepare well-dispersed nanoparticle colloid. In the present study, cobalt nanoparticles (∼15 nm in size) were synthesized with the fatty acid (oleic acid) as a surfactant. The chemical interaction of the surfactant with the Co nanoparticles was studied by using Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The results indicated that oleic acid gets chemisorbed as a carboxylate on the Co nanoparticle surfaces, and the two oxygen atoms in the carboxylate are coordinated symmetrically to the Co atoms, leading to the formation of the covalent Co−O bond. This result has implications for the strong interaction between the surfactant and Co nanoparticle, which enhances the stability of Co colloid.