The Effect of Water on the Work of Adhesion at Epoxy Interfaces by Molecular Dynamics Simulation

Molecular dynamics simulation can be used to explore the detailed effects of chemistry on properties of materials. In this paper, two different epoxies found in aerospace resins are modeled using molecular dynamics. The first material, an amine-cured tetrafunctional epoxy, represents a composite matrix resin, while the second represents a 177°C-cured adhesive. Surface energies are derived for both epoxies and the work of adhesion values calculated for the epoxy/epoxy interfaces agree with experiment. Adding water-- to simulate the effect of moisture exposure-- reduced the work of adhesion in one case, and increased it in the other. To explore the difference, the various energy terms that make up the net work of adhesion were compared and the location of the added water was examined. Nomenclature W = work of adhesion Efilm,1 = configurational energy of thin film of Epoxy 1 Efilm,2 = configurational energy of thin film of Epoxy 2 Einterface = configurational energy of the interface Ewater-water = configurational energy of the water-water interaction Ewater-epoxy = configurational energy of the water-epoxy interaction A = cross-sectional area I