Yield and Post-yield Behavior of Fatty-Acid-Functionalized Amidoamine-Epoxy Systems: A Molecular Simulation Study

The effect of alkyl chain in the amidoamine crosslinker on the yield and post-yield behavior using non-equilibrium molecular dynamics simulation is studied in this work. Specifically the deformation behavior of two thermosets with and without the alkyl chain are simulated. The yield stress and strain hardening modulus were predicted. It was found that the thermoset with alkyl chain had lower yield stress and strain hardening modulus compared to the one without. Stress partitioning revealed that intermolecular Lennard-Jones (LJ) and covalent interactions contribute significantly to the yield stress and strain hardening modulus in these thermosets while the electrostatic interactions have no significant effect on both. The effect of methylene interactions on the yield and post-yield behavior were also investigated. It was found that the lower yield stress in the thermoset with alkyl chain is due to the dilution effect and the decrease in strain hardening modulus is due to both dilution effect and intramolecular LJ interactions of methylenes. Simulations reveal a trade off between dilution effect and covalent interactions of the system which can be utilized to tune the mechanical properties of thermosets. The major contribution of this work is the computational approach that can be used to discover the effect of additives or other molecular constituents on the deformation characteristics of a thermoset regardless of the deformation mode tensile or compressive.