Fully atomistic molecular dynamics (MD) simulations have been carried out on a series of
bulk melt pure PEO oligomers and PEO oligomer−silica systems, which differed by their macromolecular
end groups. A realistic hybrid model of a silica nanoparticle combining an ionic core as well as the fine-tuning of the surface thickness and number of OH groups per unit surface area was used. The PEO
oligomers were decorrelated in all systems under study in order to prevent any artifacts related to the
preparation procedure. Significant changes were found to occur in the immediate vicinity of the interface
with flattened PEO backbones arranged in densily packed shells and stabilized by the added PEO−silica
interactions. Their conformations were also more coiled in order to better adapt to the surface structure.
While methyl end groups did not show special characteristics other than their steric effect, hydroxyl end
groups had a much higher affinity for the surface and tended to position themselves perpendicular to the
surface, thus forming dynamic hydrogen-bonding complexes between the hydroxyl oxygens and the silanol
hydrogens. The range of influence of the nanoparticle was evident for structural properties only up to
two or three molecular layers, 10−15 Å, but was approximately twice that for dynamical ones.
The more or less peaty muds, which formed sediments from the Mesolithic period in the Erve valley (Mayenne) and which have preserved the pollen archives, record the evolution of vegetation up to recent times. The first traces of human impact were detected from the Middle Neolithic, but became more important in the Late Neolithic and intensified during the second half of the Bronze Age. The Middle Ages marked a radical change in agro-pastoral practices with the development of cereal growing and hemp cultivation, the appearance of walnut, chestnut, buckwheat, flax and perhaps the cultivation of vines. The present boxtree plantings seem to have their origins in the central Middle Ages.
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