H bond spring behaviour in hybrid silica under pressure
Résumé
Bridged silsesquioxane nanomaterials exhibit original mechanical properties thanks to the association of non-covalent and covalent interactions. Thanks to in situ high pressure spectroscopic studies, achieved in diamond anvil cells, the mechanical behavior of these materials was followed as a function of pressure.
Figure 1: Schematic representation of bottom-up structuring in organic-inorganic hybrid silica through self-assembling process
Vibrational studies on organic models coupled to ab-initio simulations show that H bond response to pressure is strengthening. In hybrid materials the H bond shows its ability to absorb the mechanical constrains by the modulation of H bond interactions. We thus show that the rigidity yielded by the inorganic polymerization is counterbalanced by the presence of the intermolecular H bond network. The hybrid materials have therefore a reversible behavior, thanks to h bonds behaving as molecular springs. For higher pressure ranges inorganic network start to be strongly impacted in a dominant way so that an irreversible loss of long range order within the organic network is observed.
In a second time, the influence of the nature of the organic substructure (thiourea versus urea link, aryl versus aliphatic core) on this spring behavior is discussed.