Molecular dynamics research on interfacial reinforcement between ε-CL-20 and polymeric bonding agents for humidity-insensitive solid propellant systems

The triazole curing systems of solid propellants have the advantage of unique humidity-insensitivity. For the popular high-energy oxidizer of ε-CL-20, the matched neutral polymeric bonding agents (NPBAs) might play a key role on enhancing mechanical properties of triazole-cured solid propellant by encapsulating oxidizer particles to promote the interaction with binder. Based on the structural design and composition regulation of the typical NPBA, alkynyl-containing copolymers were designed for triazole-cured energetic systems, and their interaction behaviors with ε-CL-20 have been simulated by molecular dynamics. Compared with the urethane-curing system based on NPBAs without alkynyl groups, we found that the presence of alkynyl groups in polymer chains, which designatedly reacted with the azide-containing binder, could reinforce the interface strength directly by 12.43%. Furthermore, the results of radial distribution function (RDF) indicated the interface interaction between ε-CL-20 and NPBAs was mainly attributed to electrostatic adsorption, and about 2 hydrogen bonds were formed between the nitro groups of ε-CL-20 and the NPBA with 11 hydroxyl groups. This research strategy of predicting interfacial interaction between polymer and small molecules is valuable for the development of the structural design of polymeric bonding agents, and even the mechanical optimization and application of ε-CL-20-based energetic composites.