Adhesive strength is known to change significantly depending on the direction of the force applied. In this study, the peel and tensile adhesive forces between the hydroxylated silica (001) surface and epoxy resin are estimated based on quantum chemical calculations. Here, density functional theory (DFT) with dispersion correction is used. In the peel process, the epoxy resin is pulled off from the terminal part, while in the tensile process, the entire epoxy resin is pulled off vertically. As a result of these calculations, the maximum adhesive force in the peel process is decreased to be about 40% of that in the tensile process. The adhesion force–displacement curve for the peeling process shows two characteristic peaks corresponding to the process where the adhesive molecule horizontally oriented to the surface shifts to a vertical orientation to the surface and the process where the vertical adhesive molecule is dissociated from the surface. Force decomposition analysis is performed to further understand the peel adhesion force; the contribution of the dispersion force is found to be slightly larger than that of the DFT force. This feature is common to the tensile process as well. Each force in the peel process is about 40% smaller than the corresponding force in the tensile process.

Adhesive strength varies greatly with direction; various adhesion tests have been conducted. In this study, the shear and tensile adhesive strength of epoxy resin for copper (Cu) and copper oxide...

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.