Abstract
The transport properties of oxygen in three amino-functionalized cubic polyhedral oligomeric silsesquioxanes (POSS)
have been studied using classical mol. dynamics (MD) simulations over a timescale long enough to reach the Fickian
regime for diffusion. An amt. of O2 corresponding to an applied pressure of 3 bars was inserted into mol. models of
hybrid org./inorg. POSS with the chem. compn. (RSiO3/2)8, which differed by the end-groups of their org. pendant chains,
i.e., R = -(CH2)3-NH-CO-X with X = -C6H4OH, -C6H5 or -C6H11. The oxygen ... POSS energies were found to be small
with respect to the POSS... POSS interactions. The O2 mols. permeate the org. phase and move through combinations
of oscillations within available free vols. in the matrixes and occasional jumping events. Gas mobility was more restricted
in the system with the salicylic end-group and the largest hydrogen-bond network, whereas it was enhanced in the
system with the cyclohexyl end-group. The most energetically-favorable sites for O2 insertion were either in the vicinity
of the silica cages or close to the rings of the chain end-groups. On the other hand, the amide and hydroxyls groups
engaging in H-bonds were less energetically favorable. This confirms that H-bonding networks are a hindrance for O2
transport in such systems.
have been studied using classical mol. dynamics (MD) simulations over a timescale long enough to reach the Fickian
regime for diffusion. An amt. of O2 corresponding to an applied pressure of 3 bars was inserted into mol. models of
hybrid org./inorg. POSS with the chem. compn. (RSiO3/2)8, which differed by the end-groups of their org. pendant chains,
i.e., R = -(CH2)3-NH-CO-X with X = -C6H4OH, -C6H5 or -C6H11. The oxygen ... POSS energies were found to be small
with respect to the POSS... POSS interactions. The O2 mols. permeate the org. phase and move through combinations
of oscillations within available free vols. in the matrixes and occasional jumping events. Gas mobility was more restricted
in the system with the salicylic end-group and the largest hydrogen-bond network, whereas it was enhanced in the
system with the cyclohexyl end-group. The most energetically-favorable sites for O2 insertion were either in the vicinity
of the silica cages or close to the rings of the chain end-groups. On the other hand, the amide and hydroxyls groups
engaging in H-bonds were less energetically favorable. This confirms that H-bonding networks are a hindrance for O2
transport in such systems.
