# MD-DFT Calculations on Dissociative Absorption Configurations of FOX-7 on (001)- and (101)-Oriented Crystalline Parylene Protective Membranes

## TL;DR

This paper uses MD and DFT to study how FOX-7 interacts with parylene membranes, revealing that electrostatic interactions and hydrogen bonding help reduce explosive sensitivity.

## Contribution

The study identifies -NO2–π electrostatic interactions and H-bond formation as key passivation mechanisms for FOX-7 on parylene surfaces.

## Key findings

- FOX-7 dissociatively adsorbs on parylene membranes via LUMO-HOMO interactions and H-bond formation.
- (001)-oriented parylene AF8 is effective in passivating high-energy -NO2 bonds of FOX-7.
- Decomposition occurs through C-NO2 bond fission and nitro-to-nitrite rearrangement during adsorption.

## Abstract

Crystalline poly-para-xylylene (parylene) has the potential for use as a protective membrane to delay the nucleation of explosives by separating the explosives and their decomposition products to decrease the explosive sensitivity. Here, molecular dynamics (MD) and density functional theory (DFT) techniques were used to calculate the dissociative adsorption configurations of 1,1-diamino-2,2-dinitroethylene (FOX-7) on (001)- and (101)-oriented crystalline parylene membranes. Based on the results of the calculations, this work demonstrates that the -NO2–π electrostatic interactions are the dominant passivation mechanism of FOX-7 on these oriented surfaces. FOX-7 can dissociatively adsorb on oriented parylene membranes due to the interactions between the LUMO of the toluene (or methyl) groups on parylene and the HOMO of the -NO2 (or -NH2) groups on FOX-7. The formation of a new intermolecular H-bond with the ONO group leads to FOX-7 decomposition via intramolecular C-NO2 bond fission and nitro-to-nitrite rearrangement. The most likely adsorption configurations are described in terms of the decomposition products, surface active groups of parylene, binding behaviors, and N charge transfer. Importantly, the (001)-oriented parylene AF8 membrane is promising for use as a protective membrane to passivate the high-energy -NO2 bonds during the dissociative adsorption of FOX-7. This study offers a new perspective on the development of protective membranes for explosives.