Tuning the Molecular Topology of Polymeric Materials for Superior Ballistic Performance
Abstract
The objective of this research is to discover materials with superior ballistic performance by tailoring the molecular topology of polymers and polymer-grafted nanoparticles. For impact and ballistic protection materials used in soft body armor and transparent armor, polymeric systems that exhibit high stiffness, strength and energy dissipation when subject to high strain rate deformation are critically needed. This project will address this need by moving beyond linear polymer chains and exploring branched polymer topologies; namely stars, bottlebrushes and polymer grafted systems such as assembled hairy nanoparticles (aHNPs), which form neat single-component materials. This project will improve the understanding of the mechanics of branched polymers, by establishing coarse-grained and meso-scale representations for molecular dynamics simulations of these systems to predict mechanical behavior in bulk and in thin films. To pursue the overarching objective, this project involves two research thrusts. Thrust 1 will investigate polymer topology and specimen size-effects on ballistic performance, focusing on the mechanics of star and bottle-brush polymers. Thrust 2 will focus on the design of assembled hairy nanoparticles (aHNPs) for greater high-strain rate toughness. Complex topologies in polymers offer a wide parametric design space that allows diametric mechanical properties such as strength and toughness to be jointly optimized, which is critical for improving ballistic performance. Recent investigations suggest that branched polymers can exhibit novel toughening mechanisms and display strain-rate or temperature dependent phenomena not seen in linear polymers. It is envisioned that branched polymers can exhibit tunable shear-thickening, which can strengthen interfaces and provide greater energy dissipation in polymer films and fibers. This research will aim to address key knowledge gaps in the field. The central question to be addressed is how the molecular topology must be tailored for programming constitutive behavior at high-strain rates. This will be done by carrying out molecular simulations mimicking laser-induced projectile impact tests (LIPIT), along with other mechanical characterizations to understand topology and size-effects. This project builds upon the PIÕs prior contributions to systematic coarse-graining of polymeric materials for studying the mechanics and ballistic response of polymer thin films. To capture chemical specificity, interface and size effects with greater efficiency at the scale of thin films, new multi-scale models based on energy renormalization-based coarse-graining and interparticle potentials of mean force will be established in this project. The computational methods and insights developed will accelerate the discovery of high-performance polymer materials for ballistic protection. Polymeric thin films and coatings that have superior high-strain rate properties are critically needed for soft body armor, electronic packaging, safer batteries, and structural nanocomposites. The project will shed light on how polymer and aHNP topology influences their constitutive behavior, which is a new direction of inquiry within the solid mechanics community. Discovery of tunable viscosity, one-component shear-thickening polymeric materials that have no additional carrier medium has the potential to create a paradigm shift in armor materials. The proposed research will cement ongoing collaborations with national labs including NIST, ARL-Central and ARL-APG on impact physics of polymeric materials. This work will advance computational capabilities by establishing methods and new physical insights required for the mechanical design of topologically complex polymeric materials.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Sep 28, 2022
- Source ID
- W911NF2210287
Entities
People
- Sinan Keten
Organizations
- Army Contracting Command
- Northwestern University
- United States Army