Multilayer Deposition of Metal–Phenolic Networks for Coating of Energetic Crystals: Modulated Surface Structures and Highly Enhanced Thermal Stability

Abstract

Phase transition under thermal stimulation remains a long-standing problem for practical applications of polymorphic energetic crystals such as 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX). Herein, tannic acid (TA)-based metal−phenolic networks (MPNs), an emerging class of coatings formed through coordination chemistry, were introduced to improve the thermal stability of energetic HMX. Detailed characterizations were systematically conducted and confirmed the formation of a compact core−shell structure upon in situ noncovalent decoration of polyphenols and Fe III under ambient conditions. Additionally, the dynamic nature of MPNs assembly facilitated multilayer deposition with tunable coverage and thickness. As a result, the phase transition (β → δ) temperature of optimized HMX@MPNs was significantly improved by 42.3 °C at low coating loadings (1.8 wt %), as revealed by thermogravimetry−differential scanning calorimetry (TG−DSC) and in situ X-ray diffraction (XRD) techniques. On this basis, an in-depth understanding of the phasetransition mechanism was achieved by employing isothermal kinetics modeling. This work demonstrates a facile and robust coating strategy for modularized surface engineering of energetic crystals, resulting in remarkably enhanced thermal stability.

Interaction‐Enhanced Coating of Energetic Material: A Generally Applicable Method for the Desensitization

“…And when the ratio of Am−GO : G is 0.5 : 1.5, the composite has the best mechanical sensitivity. To our best knowledge, this mechanical sensitivity is the most insensitivity compared to the previous reports prepared by coating desensitization with non‐energetic desensitized material [18–24]. Especially, the addition amount of desensitized material in this preparation is strictly controlled to 2 wt%, which also is less than most previous reports.…”

“…At present, the most practical method of desensitization is the coating technology [13][14][15][16][17][18][19][20][21][22][23][24]. And carbon materials have been widely utilized to reduce the sensitivity for their unique structure and excellent physical and chemical properties [6,[25][26][27].…”

Assembly of Metal–Phenolic Networks on Water‐Soluble Substrates in Nonaqueous Media

“…Analysis of the Fe III -TA solution after the addition of urea granules revealed a characteristic LMCT band at ≈565 nm (Figure 2a), confirming the formation of Fe III -TA complexes. [41] The analytical data suggest that several factors contribute to Fe III -TA particle formation in acetonitrile following the addition of urea granules. First, the amine group of dissolved urea (NH 2 ) in acetonitrile (the solubility of urea in acetonitrile is ≈4 g L −1 at room temperature) can play a role in the formation of intermediates between the hydroxyl groups of TA and water molecules of FeCl 3 •6H 2 O via hydrogen bonding.…”

The Art of Framework Construction: Core–Shell Structured Micro-Energetic Materials

“…Metal-phenolic networks (MPNs) are an emerging class of supramolecular coatings formed through coordination chemistry, which have strong adhesive attachment to diverse organic surfaces [ 44 ]. Tannic acid (TA)-based MPNs were utilized to coat HMX via in situ noncovalent decoration of polyphenols and Fe III as shown in Figure 12 [ 65 ]. HMX surface was regularly coated through layer-by-layer deposition and the thickness of coating could be controlled by tuning the coating cycles.…”

“… ( a ) Molecular structures of the typical energetic molecules HMX and CL-20; ( b ) Schematic representation of the preparation of the surface-modified energetic crystal via multilayer deposition of MPNs. Reproduced with permission from [ 65 ], copyright 2020, Elsevier. …”