A combined coarse-graining and back-mapping approach to preparing relaxed systems of amorphous polymers with atomistic detail is presented and applied to the case of bulk amorphous cellulose. The coarse-grained model is first developed using results from a standard molecular dynamics atomistic simulation of octaose, i.e., the short 8-ring oligomer of cellulose. The change to a coarse-grained scale leads to an effective speed-up in excess of 2000 for the computational efficiency of the relaxation of the chains. A representation of one ring by one bead is used in order to maintain a good description of the envelope of the molecule and this allows for a subsequent seamless reintroduction of the atoms. The back-mapping procedure has been successfully tested on dense bulk systems of both octaose and hectaose, i.e., 100-ring cellulose chains. The principal advantage and motivation for this approach is that it adapts well to cases where interfaces are present and spatial isotropy of chain conformations is no longer assured or easily predictable.

International audienceNanostructured hybrid silicas, in which covalently anchored aromatic thiols are regularly distributed over the pores, enable a dramatic increase in the half-lives of the corresponding arylsulfanyl radicals. This enhancement is not only due to limited diffusion but also to the structure of the organic monolayer on the surface of the pores. Molecular dynamics modeling shows that at high loadings, in spite of their spatial vicinity, supramolecular interactions disfavor the coupling of arylsulfanyl radicals. As compared to phenylsulfanyl radical in solution, the half-life measured at 293 K can be increased by 9 orders of magnitude to reach 65 h