The adhesion mechanism of epoxy resin (ER) cured material
consisting
of diglycidyl ether of bisphenol A (DGEBA) and 4,4′-diaminodiphenyl
sulfone (DDS) to pristine graphene and graphene oxide (GO) surfaces
is investigated on the basis of first-principles density functional
theory (DFT) with dispersion correction. Graphene is often used as
a reinforcing filler incorporated into ER polymer matrices. The adhesion
strength is significantly improved by using GO obtained by the oxidation
of graphene. The interfacial interactions at the ER/graphene and ER/GO
interfaces were analyzed to clarify the origin of this adhesion. The
contribution of dispersion interaction to the adhesive stress at the
two interfaces is almost identical. In contrast, the DFT energy contribution
is found to be more significant at the ER/GO interface. Crystal orbital
Hamiltonian population (COHP) analysis suggests the existence of hydrogen
bonding (H-bonding) between the hydroxyl, epoxide, amine, and sulfonyl
groups of the ER cured with DDS and the hydroxyl groups of the GO
surface, in addition to the OH−π interaction between
the benzene rings of ER and the hydroxyl groups of the GO surface.
The H-bond has a large orbital interaction energy, which is found
to contribute significantly to the adhesive strength at the ER/GO
interface. The overall interaction at the ER/graphene is much weaker
due to antibonding type interactions just below the Fermi level. This
finding indicates that only dispersion interaction is significant
when ER is adsorbed on the graphene surface.
Graphene is a highly promising material in the field of spin electronics. Recent experiments on electron spin resonance have observed a reduction in the g-factor of graphene. In this paper, we focus on the Rashba effect, which is caused by the work function existing near the surface of graphene. The Rashba effect tilts the spin magnetic moment to the in-plane direction of the graphene sheet, potentially reducing the g-factor. We evaluate this reduction using a simple model system incorporating the Rashba and spin Zeeman effects. We then demonstrate that the resultant g-factor is in close agreement with that observed in the prior experiments, indicating that the Rashba effect is able to account for the remaining reduction in the g-factor of graphene.
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