(134f) Atomistic Simulations of Structure and Mechanical Behavior of Primed and Unprimed Epoxy-Alumina Interfaces

The nature of the adhesive bonding between crosslinked thermosetting resins and inorganic or metallic substrates plays a critical role in a variety of materials applications including fiber or particle reinforced composites and bonding of metal parts in the aerospace and automotive industries. In the simpler cases, bonding between the organic and inorganic or metal components occurs via van der Waals dispersive and electrostatic interactions.  However, frequently, additional primer compounds are introduced to form chemical bonds at the interface between the major system components.

In recent work, we have performed a series of investigations of the properties of crosslinked thermosets, including studies of the effect of resin architecture on small strain elastic constants and gelation studies in polyester and epoxy systems (1), which show good quantitative agreement with available experimental data.  Accordingly we now perform extensions of these calculations to include interfaces with a solid substrate.  Specifically, the present work focuses on model adhesive type systems in which crosslinked epoxy interacts with an alumina substrate similar to that produced by anodization pretreatment of surfaces prior to assembly using adhesives. Two types of model systems are considered, with the first containing only crosslinked epoxy and alumina, and the second containing in addition the commonly-used primer gamma-aminopropyltriethoxysilane in which the ethoxysilane moieties have been pre reacted with the alumina substrate prior to performing the amine-based crosslinking with the epoxy resin and curing agent.

Following the model building, the epoxy-alumina interface systems are equilibrated using the MedeA^®-LAMMPS simulation environment (2, 3) before being to subjected to structural analysis to elucidate the nature of packing at the interface, accompanied by mechanical property calculation to compare and contrast the behavior of the systems when subjected to small and large deformations.  Finally, we report on possible interface failure mechanisms by analyzing the model behavior at large deformations.

1. D. Rigby, C.M. Freeman, P.W. Saxe and B. Leblanc, Computational Prediction of Mechanical Properties of Glassy Polymer Blends and Thermosets, Proceedings of the 143rd Annual TMS Meeting, San Diego, CA, Feb 16-20, 2014.
2. Materials Design, Inc.; http://www.materialsdesign.com/medea
3. S. Plimpton, Fast Parallel Algorithms for Short-Range Molecular Dynamics, J Comp Phys, 117, 1-19 (1995); http://lammps.sandia.gov