# Molecular Simulations of Interface-Driven Crosslinked Network Formation and Mechanical Response in Composite Propellants

## TL;DR

This study uses molecular simulations to understand how different components in composite propellants interact and affect mechanical properties, offering insights for better propellant design.

## Contribution

The paper introduces a computational framework combining coarse-grained simulations and reactive force fields to study interfacial interactions in composite propellants.

## Key findings

- A two-step reaction mechanism was identified at the AP interface involving self-polymerization and crosslinking.
- Optimized parameters led to a ~20% improvement in tensile modulus and strength of the propellants.
- Key factors like HTPB chain length and IPDI content significantly influence mechanical performance.

## Abstract

Composite solid propellants, which serve as the core energetic materials in aerospace and military propulsion systems, necessitate tailored enhancement of their mechanical properties to ensure operational safety and stability. A critical challenge involves elucidating the interfacial interactions among the multiple propellant components (≥6 components, including the polymer binder HTPB, curing agent IPDI, oxidizer particles AP/Al, bonding agents MAPO/T313, plasticizer DOS, etc.) and their influence on crosslinked network formation. In this study, we propose an integrated computational framework that combines coarse-grained simulations with reactive force fields to investigate these complex interactions at the molecular level. Our approach successfully elucidates the two-step reaction mechanism propagating along the AP interface in multicomponent propellants, comprising interfacial self-polymerization of bonding agents followed by the participation of curing agents in crosslinked network formation. Furthermore, we assess the mechanical performance through tensile simulations, systematically investigating both defect formation near the interface and the influence of key parameters, including the self-polymerization time, HTPB chain length, and IPDI content. Our results indicate that the rational selection of parameters enables the optimization of mechanical properties (e.g., ~20% synchronous improvement in tensile modulus and strength, achieved by selecting a side-chain ratio of 20%, a DOS molar ratio of 2.5%, a MAPO:T313 ratio of 1:2, a self-polymerization MAPO time of 260 ns, etc.). Overall, this study provides molecular-level insights into the structure–property relationships of composite propellants and offers a valuable computational framework for guided formulation optimization in propellant manufacturing.