Computational study of fluorinated nanodiamonds: Thermodynamics, electronic structure and interaction with PMMA

Fluorinated nanometer-scaled diamond particles (NDs) C26F32, C84F64 and C148F96 have been theoretically investigated using the dispersion-corrected density functional theory. We justify that fluorinated NDs are more thermodynamically stable than fluorinated fullerenes of comparable size due to the stronger C-F bonds. Consequently, NDs are also more resistant to defluorination. The differences in lengths and energies of C-F bonds formed on the NDs edges and surfaces are discussed in details. We observe that fluorine atoms contribute significantly to both frontier molecular orbitals of fluorinated NDs. The HOMO-LUMO gap has a tendency to decrease with the ND size. The electron density transfer from the carbon core to the fluorine shell is found to be about 0.1 electrons per fluorine atom. Global optimization of the polymethyl methacrylate (PMMA) + ND configuration have been carried out with the genetic algorithm. A weak interaction of fluorinated NDs with PMMA polymer has been established. The concrete value and sign of the binding energy depends on the ND size. The electronic orbitals of NDs almost do not hybridize with those of the PMMA, so the optical properties of NDs into the polymer matrix remain unchanged. The paper discusses the effect of ND coating with fluorine and other functional groups on the mechanical and optical characteristics of the resulting NDs / polymer composite.