Molecular Understanding of Adhesion of Epoxy Resin to Graphene and Graphene Oxide Surfaces in Terms of Orbital Interactions

Abstract

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.

Effects of Curing Agents on the Adhesion of Epoxy Resin to Copper: A Density Functional Theory Study

“…To reduce computational cost, the effect of relaxation of the molecular structure as the molecules move away from the surface was neglected. Since the higher the loading rate, the greater the breaking force, the values of adhesion stress presented in this paper should be understood as those in the fast limit of pulling apart. , Thus, our theoretically predicted values of adhesive stress tend to be larger than those actually measured experimentally under finite loading rate conditions. The energy of each structure was calculated, and the Morse potential curve was calculated using eq : E = D e false( 1 − normale − a normalΔ r false) 2 where Δ r is the distance that the resin fragment is pulled away from the adherend surface, D e is the adhesion energy, and a is a constant that determines the width of the potential energy well; D e and a were determined by least-squares fitting.…”

Elucidating the Effects of Chemisorbed Water Molecules on the Adhesive Interactions of Epoxy Resin to γ-Alumina Surfaces

“…The dissociation energy curves of the FER molecule for the four FER/alumina interfaces ( 1b , 2b , 3b , and 4b ) are shown in Figure a. These energy curves have a single inflection point, which corresponds with previous studies. ,,,− ,− The black, blue, orange, and red colors correspond with the dissociation energy curves of the FER for 1b , 2b , 3b , and 4b , wherein the points on the curves are the calculated values and the solid lines are the fitting curves for the Morse potential expressed in eq . The parameter D e of the Morse potential represents the adhesion energy, that is, the depth of the potential well, which was 3.22, 2.94, 2.30, and 2.96 eV, respectively.…”

“…(2) and (3) in Figure show the OH−π interactions between the phenyl groups of the FER molecule and hydroxy groups on the alumina surface with ICOHP values of −0.22 and −0.13 eV, respectively. Although these OH−π interactions are not strong, their contribution to adhesion is expected to increase as the degree of polymerization of the epoxy resin increases because the epoxy resin backbone contains numerous benzene rings. , The total ICOHP value is −5.29 eV, wherein the strength of the interfacial interaction is 1b > 4b > 2b > 3b . This result corresponds to the order of adhesion strength and supports the notion that interactions involving charge transfer are key at these interfaces.…”

Molecular Understanding of the Distinction between Adhesive Failure and Cohesive Failure in Adhesive Bonds with Epoxy Resin Adhesives

“…Note that the relationship between the two layers of epoxy molecules is assumed to be static in the adhesive failure model, while the relationship between the lower epoxy molecule and the SAM surface is static in the cohesive failure model. Therefore, the adhesive force obtained from such sequential single-point calculations corresponds to the adhesive force when the epoxy molecule is rapidly pulled away from the surface, which allows one to estimate the upper limit of the adhesive force . It has recently been reported that the results obtained with the above simulation methods are in qualitative agreement with those obtained from experiments .…”

“…The adhesion forces at the interface between the epoxy resin model and the SAM surface and between the epoxy molecules in the epoxy resin model were calculated according to previous studies. , One epoxy molecule or two epoxy molecules were pulled upward in steps of 0.2 Å from 0 to 10 Å. At each step, a single-point calculation was performed to determine the potential energy ( E ) of the system.…”