Atomistic-scale modeling of nano-clay-filled shape memory polymers

Abstract Shape memory polymers (SMPs) have been defined as materials that can recover an early programmed shape after subjecting to an external stimulus. The epoxy/clay nano-composites are developed as a mix of shape recovery behavior and improved thermomechanical properties. The epoxy/clay interface zone plays a big role in material failure. The existence of multiple material phases, as well as multiple interaction forces that interact phases with each other, make the interface zone very complicated to study and simulate. Furthermore, such a tiny size zone is very hard to characterize using the conventional experiment types of equipment. Therefore, the Molecular Dynamics method (MD) has come to light as an effective simulation method to study the atomistic scale dynamic material phenomena. In this work, the MD method is employed to evaluate the thermomechanical performance of the epoxy/clay nano-composites at the atomistic scale level. The estimated elastic parameters confirmed the improvement of the thermomechanical properties of the epoxy/clay nano-composites. Furthermore, the transition temperature and the thermal expansion coefficient are included inside the MD simulation for both the pure epoxy polymer and epoxy/clay nano-composites. The computed above-mentioned parameters are in fairly good agreement with the experimental observations that make these calculated parameters generally appropriate for use at a higher length scale level model. In addition, the response of the epoxy/clay interface zone under mechanical load was also investigated for different silicate layer orientations, namely, 0°, 20°, 45°, 70°, and 90° aligned to the external uniaxial load. The main cohesive parameters like cohesive stiffness, cohesive strength, and maximum separation are derived numerically for every silicate layer orientation. The resulting traction-separation curves of the interface zone provided a deep understanding of the material failure initiation. Moreover, the cohesive zone model parameters are estimated and parameterized in equations with the silicate layer orientations to use in a multiscale modeling framework.