Multilayered core-shell structure of polyol-stabilized calcium fluoride nanoparticles characterized by NMR

Diethyleneglycol (DEG)-stabilized calcium fluoride (CaF(2)) nanoparticles with a mean diameter of about 20 nm consist of an inorganic crystalline core, covered by a roughly monomolecular layer of organic material according to standard physico-chemical analysis. Multinuclear NMR experiments under magic angle spinning were used to identify the constituent (13)C, (1)H and (19)F atoms. All resonances were assigned (DEG, EtOH, H(2)O, H(3)O(+), OH(-), F(-), CaF(2)), and different populations could be discriminated in terms of their mobilities and correlations with neighboring atoms. We observed several different layers: mobile EtOH on the particle surface, an "interphase" containing immobile DEG molecules and fluoride ions, plus the single-crystalline CaF(2) core. It was thus possible for the first time to characterize by NMR all layered components of such core-shell particles, and the thickness of the newly discovered interphase could be estimated from the NMR intensities.