Block Chemistry for Accurate Modeling of Epoxy Resins

Abstract

Accurate molecular modeling of the physical and chemical behavior of highly cross-linked epoxy resins at the atomistic scale is important for the design of new propertyoptimized materials. However, a systematic approach to parametrizing and characterizing these systems in molecular dynamics is missing. We therefore present a unified scheme to derive atomic charges for amine-based epoxy resins, in agreement with the AMBER force field, based on defining reactive fragments� blocks�building the network. The approach is applicable to all stages of curing from pure liquid to gelation to fully cured glass. We utilize this approach to study DGEBA/DDS epoxy systems, incorporating dynamic topology changes into atomistic molecular dynamics simulations of the curing reaction with 127,000 atoms. We study size effects in our simulations and predict the gel point utilizing a rigorous percolation theory to recover accurately the experimental data. Furthermore, we observe excellent agreement between the estimated and the experimentally determined glass transition temperatures as a function of curing rate. Finally, we demonstrate the quality of our model by the prediction of the elastic modulus based on uniaxial tensile tests. The presented scheme paves the way for a broadly consistent approach for modeling and characterizing all amine-based epoxy resins.

Segregation in epoxy/amine systems on iron oxide surfaces

“…24 Different methods have been reported in the literature to calculate charges of atoms in epoxy amine polymers. 25–27 The method used in this work has shown to give correct thermal and mechanical properties of the polymer, 25 and in simulations used to parameterise coarse grain models that were successfully used to calculate glass transition temperatures. 26 Other methods reported in the literature are also able to accurately reproduce experimental observations, 27 but it is beyond the scope of the paper to compare the advantages and disadvantages of the different methods available.…”

Dielectric Properties of Benzocyclobutene-Based Resin: A Molecular Dynamics Study

“…The polymers studied have complex cross-linking paths and modes, and although Lammps provides cross-linking functionality, it is often not applicable to some of the polymer systems studied. For example, direct cross-linking in Lammps using the Fixed Bond/Create or Fixed Bond/React commands may cause warning problems due to periodic boundary conditions, and therefore, we did not adopt the approach of Livraghi et al We perform all-atom molecular dynamics simulations based on BCB-based resins using the epoxy cross-linking script as a basis, improve the script to make it suitable for BCB-based resin systems, and then perform relaxation calculations by invoking Lammps in the script. The specific cross-linking simulation protocol is described in detail in the following simulation flow.…”