The supermolecular structures found in cured epoxy resins

Abstract

Abstract The work arose from the need to explain the beneficial effect of post‐curing at an elevated temperature on the strengths of lap‐shear joints made with amine‐cured epoxy resins. Supermolecular structures were imaged by several electromicroscopy techniques, usually at 100,000 X. Three, if not four, stages of supermolecular structure were made visible. (i) A phase‐contrast image of 1.3 to 2.1 nm diameter which are probably stacked residues of bisphenol A. The d‐spacing seen in the diffracting mode of the microscope probably arises from within this structure. (ii) A nodular structure of ca. 5 nm. (iii) Aggregates of nodules of ca. 17 nm rising to 40 n m on post‐cure. These dimensions were obtained from cumulative distributions of sizes based on photodensitometer records from the electron‐micrograph negatives. Aggregate dimensions vary with curing agent and state of cure although minor variations occur with specimen preparation.