Initial Curing Process between Epoxy and Amine at a Solid Interface

A chemical reaction between epoxy and amine compounds at a solid interface is of pivotal importance for the manifestation of the adhesion strength.  Here we examined the initial curing reaction of epoxy phenol novolac (EPN) and 4,4'-diaminodiphenyl sulfone (DDS) at a quartz interface using sum-frequency generation spectroscopy.  The reaction rate constant (k) at the quartz interface was much larger than in the bulk.  The Arrhenius analysis of k revealed that while the activation energy was identical to each other, the frequency factor was much larger at the interface than in the bulk.  The faster curing reaction at the interface was also confirmed for different system of diglycidyl ether of bisphenol A (DGEBA) and DDS.  The results might be explained in terms of a better orientation ordering and/or the densification of reactants at the interface, facilitating the encounter of the reactants there.