The glass transition in cured epoxy thermosets: A comparative molecular dynamics study in coarse-grained and atomistic resolution

Abstract

We investigate the volumetric glass transition temperature Tg in epoxy thermosets by means of molecular dynamics simulations. The epoxy thermosets consist of the resin bisphenol A diglycidyl ether and the hardener diethylenetriamine. A structure based coarse-grained (CG) force field has been derived using iterative Boltzmann inversion in order to facilitate simulations of larger length scales. We observe that Tg increases clearly with the degree of cross-linking for all-atomistic (AA) and CG simulations. The transition Tg in CG simulations of uncured mixtures is much lower than in AA-simulations due to the soft nature of the CG potentials, but increases all the more with the formation of rigid cross-links. Additional simulations of the CG mixtures in contact with a surface show the existence of an interphase region of about 3 nm thickness in which the network properties deviate significantly from the bulk. In accordance to experimental studies, we observe that Tg is reduced in this interphase region and gradually increases to its bulk value with distance from the surface. The present study shows that the glass transition is a local phenomenon that depends on the network structure in the immediate environment.

Comparing the mechanical response of di‐, tri‐, and tetra‐functional resin epoxies with reactive molecular dynamics

“…Molecular dynamics (MD) can be used to analyze epoxies on the nanometer length‐scale to understand the influence of molecular structure on the thermo‐mechanical properties of the bulk material, as well as the interphase region arising from its usage as adhesives and composite matrices. Using MD the mechanical response of epoxies has been predicted with respect to system size, mass ratio of resin to hardener molecules, strain rate, moisture content, and temperature .…”

Routine million-particle simulations of epoxy curing with dissipative particle dynamics

“…32 takes a similar stochastic reaction approach in DPD, but shows that the conversion profiles in simulations are orders of magnitude too fast with respect to experiments. Langeloth et al achieve nearly 80% cure with CG simulations accessing as much as 32 × 10 −9 s and 10 nm length-scales 33,34 . Free radical living polymerization reaction kinetic sensitivity to bonding rates are shown in systems of 24,000 DPD spheres 35 .…”

Molecular Dynamics Simulations of Cross‐Linked Phenolic Resins Using a United‐Atom Model

“…In such cases, for studying cross‐linked phenolic and other thermosetting resins that hold experimental constraints for structural analysis, a theoretical approach based on molecular dynamics (MD) simulations is expected to be effective . Fueled by the evolution of computational sciences in polymer physics and the computational performance of desktop computers over the past two decades, many studies of epoxy resins using atomistic and coarse‐grained MD simulations have been reported and the modeling methodology of cross‐linked epoxy resins has been refined through these studies, revealing numerous molecular‐level findings that cannot be experimentally obtained . Progress in the computational studies of epoxy resins over the last two decades has mainly been the result of rapid industrial growth of carbon‐fiber reinforced plastics that use epoxy resins as matrix resins.…”