Energy Decomposition Analysis of the Adhesive Interaction between an Epoxy Resin Layer and a Silica Surface

We investigate the adhesive interaction energy (Delta E-int) between an epoxy resin and a silica surface using pair interaction energy decomposition analysis (PIEDA), which decomposes Delta E-int into four components: electrostatic (Delta E-es), exchange repulsion (Delta E-ex), charge-transfer (Delta E-ct), and dispersion (Delta E-disp) energies based on quantum chemistry. Our previous study with PIEDA showed that synergistic effects of Delta E-es and Delta E-disp are critical at the interface between an epoxy resin fragment and a hydrophilic surface. The present study is designed to show in detail that the synergistic effects are significant at the interface between an epoxy layer model consisting of 20 epoxy monomers and a hydrophilic silica surface. The ratio of the dispersion energies to the total interaction energies of the layer model shows good agreement with experimental values, that is, the dispersion ratio of the work of adhesion (Wad). The 20 epoxy molecules in the layer model are investigated individually to closely correlate the four decomposed energies with their structural features. Our energy-decomposition analyses show that H-bonding and OH-pi interactions play important roles at the interface between an epoxy resin and a silica surface. PIEDA calculations for the epoxy layer model also show that the region 3.6 angstrom from the silica surface accounts for more than 99% of the total interaction energies.

Automated summary

The study highlights the importance of synergistic effects of dispersion and electrostatic interactions at the interface between an epoxy resin and a silica surface. The ratio of dispersion energies to total interaction energies in the layer model correlates well with experimental values, showing that dispersion plays a significant role in adhesion between the two materials. Individual analysis of 20 epoxy molecules in the layer model reveals that bonding and interactions within 3.6 angstrom from the silica surface account for more than 99% of total interaction energies.