Tuning star architecture to control mechanical properties and impact resistance of polymer thin films

Abstract

Developing materials resistant to high-rate impacts requires an understanding of the molecular mechanism at play during the spatiotemporal scales of these events. Controlling the response of thin films under impact by manipulating their molecular structure is a key challenge for materials science applications and fundamental understanding of the material behavior under high-rate deformations. Using coarse-grained molecular dynamics, we tune the mobility and mechanical properties of star polymer films by varying the number of arms of the star (2≤f≤16) and their length (10≤M≤50). We subject the films to nanoballistic impacts and identify two components of the penetration energy Ep,1∗ and Ep,2∗, corresponding to the early-stage compression and late-stage deformation of the film. Ep,1∗ correlates with Young’s modulus and the Debye-Waller factor of the films, and Ep,2∗ correlates with the toughness of the films. These correlations between dynamics, mechanical properties, and ballistic resistance provide important guidelines to develop new polymer-based, impact-resistant nanomaterials.