A multinuclear solid-state magnetic resonance study of the interactions between the inorganic and organic coatings of BaSO4 submicronic particles.

Silica-coated BaSO4 submicronic particles, modified on the surface by treatment with stearic acid, have been characterized by means of 29Si, 13C, and 1H magic-angle-spinning (MAS) high-resolution techniques, and low-resolution 1H-FID analysis. Two types of adsorbed water were identified; adsorbed either inside or on the surface of BaSO4, most of the latter being removed by the silica coating. Evidences of silica-stearic acid interactions were found involving either carboxylic acid or carboxylate functional groups, and occurring by means of hydrogen and/or covalent bonds. Stearic acid was present as monolayer only, its chain being mostly rigid, even though a small fraction was subjected to fast inter-conformational motions.