Metal coordination interfacial enhancement effect: A strategy to fabricate low hygroscopic composite based on ammonium dinitramide (ADN) and polyether with enhanced mechanical properties

Abstract

Constructing and enhancing intermolecular interactions is a highly promising and versatile method for improving mechanical properties of composite materials. The application of the new green high-energy oxidizer ammonium dinitramide (ADN, NH₄⁺N(NO₂)₂^-) in composite solid propellants is often limited due to its low interfacial interaction with binders. In this study, a ferrocene derivative with ester side chains, dibutyl 1,1-Ferrocenedicarboxylic acid (FC4), was assembled on the ADN crystal surface to promote its interfacial properties. On one hand, the lone pair electron structure of dinitramide is utilized as ligand to central Fe²⁺ metal ion in ferrocene structure. On the other hand, the side chains of the ferrocene derivative enhance its van der Waals interactions with the binder. Thus, FC4 molecules act as a “bridge” to strengthen the interfacial adhesion between ADN and binder. Chemical structural characterizations and theoretical calculations confirm the existence of coordination interactions between FC4 and ADN, and the increased adsorption energy between ADN and binder. According to the experimental test results, this coordination and van der Waals force synergistic bridging effect endows the composite solid propellant with significantly enhanced tensile strength (up to 280 %), modulus (up to 305.8 %), lower hygroscopicity and sensitivity, mechanical properties of the propellant are sufficient to meet the related requirements in aerospace after the addition of FC4. This strategy provides new insights for enhancing the interfacial performance between solid fillers and binders in composite materials.