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

We investigate the adhesive interaction energy (ΔEint) between an epoxy resin and a silica surface
using pair interaction energy decomposition analysis (PIEDA), which
decomposes ΔEint into four components:
electrostatic (ΔEes), exchange repulsion
(ΔEex), charge-transfer (ΔEct), and dispersion (ΔEdisp) energies based on quantum chemistry. Our previous
study with PIEDA showed that synergistic effects of ΔEes and ΔEdisp 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−π 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 Å from the silica surface accounts for more than
99% of the total interaction energies.