Interfacial Diffusion and Bonding in Multilayer Polymer Films: A Molecular Dynamics Simulation

Abstract

As a stacked form of ultrathin polymer films, multilayer nanostructures are of great interest in various applications. Coarse-grained molecular dynamics simulations were carried out to understand the behaviors of interfacial diffusion and bonding of multilayer polymer films. We found two obvious stages for the interfacial diffusion of polymers in the multilayer film, and it is 3 times faster in the first stage than in the second one due to the evolution of molecular conformations. The polymers near the interfaces have an in-plane mobility much higher than the out-of-plane one. The strength of interfacial bonding has been characterized by the fast tensile stress-strain curve along the normal direction. It shows multiple yielding points for the multilayer polymer films, which is distinct from the tensile behavior of the bulk. The ultimate tensile stress (UTS) and corresponding separating strain, surprisingly, do not necessarily increase with diffusion time. Because of the dramatic molecular rotation and extension during the first stage of interfacial diffusion, the interlayer interpenetration is nonuniformly distributed in the plane of the interface. Such a nonuniform distribution may be one of the reasons for the decrease of the UTS and separating strain.

Mechanical and dielectric properties and crystalline behavior of multilayer graphite‐filled polyethylene composites

“…It reveals that the graphite particles gradually show a tendency of in‐plane orientation with the layer number of lamination. This phenomenon originates from the in‐plane orientation of the polymer chains near the interfaces of the multilayer structure, especially in those with ultrathin layers, which has been predicted in our previous work . This finding illustrates that the interfacial shear effect during lamination can also improve the in‐plane orientation of polymer chains and graphite particles in the multilayer structure.…”

“…Attributed to interfacial interactions in the multilayer structure and biaxial expansion, polymer chains near the interfaces would transform from curling state to being extended, ordered, and compact in the process of lamination from 3 0 to 3 6 layers . The platelet‐like graphite near the interfaces could be aligned to the plane of the interfaces in the multilayer composites.…”

“…We also simulated the evolution of graphite orientation in the polymer matrix of a single layer between two parallel walls during uniaxial and biaxial expansion to mimic the lamination process of the layer that contacts with the boundary of the laminator. Following our previous work, the molecular order parameter was calculated as where θ z is the angle between the orientation vector of the polymer chain or the normal of graphite sheet and the normal of the boundary, that is, the z ‐direction in this work. The molecular order parameters can vary from −0.5 to 0 to 1, which represent full order perpendicular to the normal, the case of isotropic orientation, and full order along the boundary normal, respectively.…”

“…Twelve graphene sheets embedded in the PE matrix was adopted in our simulations. Short chains of linear PE, instead of full length, were used following our previous work . The polymer chain consists of 100 vinyl monomers, that is, 50 C 1 ‐type CG beads with each bead representing four carbon atoms .…”

“…demonstrated that the enhancement in the breakdown strength of multilayer dielectric films is attributed to the “barrier effect,” where the multiple interfaces between the lamellae block components act as barriers to the dielectric breakdown through the film. Our recent molecular simulations revealed that the multilayer polymer films have structural heterogeneity with the chains near the interfaces orienting perpendicularly to the normal, while it is bulk‐like in the central region of each layer, so the enhancement of mechanical properties of the multilayer nanostructure is due to the increase in the number of interfacial layers and the chain orientation …”