Thin Organic Layers Grown on the Surface of Iron Particles under High-Energy Ball Milling in the Presence of Polystyrene and Various Surfactants: X-ray Absorption and Photoelectron Spectroscopy Studies

High-energy mechanical milling is conventionally and successfully used for fabrication of magnetic filler particles for metal polymer composites applied in different microwave absorption devices. Chemical modification of the metal surface by wet mechanochemical synthesis allows one to improve chemical compatibility between a metal particle and a host polymer matrix in the composites. In this paper, we have studied the structure of an as-modified thin organic layer depending on different surfactants used under mechanical milling of iron powder in the polystyrene solution. The study was performed with high-resolution X-ray spectroscopic techniques, using synchrotron radiation from the BESSY II storage ring. It has been shown that stearic acid, added as a surfactant into the milling environment, forms a close-packed thin layer, but chemical inertness of its alkyl groups does not provide strong anchoring of the polystyrene fragments to the iron surface. The perfluorononanoic acid molecules form a thin layer with preferably normal orientation of their backbones to the metal surface. The molecules are partially defluorinatecl under mechanochemical synthesis facilitating appropriate linkage between polystyrene fragments and iron. Mechanical milling with the use of perfluorinated carboxylic acids has the potential to modify the metal surface by polystyrene fragments and then to improve the chemical compatibility and adhesion between the constituents in the metal-dielectric composites.