Many-Body Mechanochemistry: Intra-molecular Strain in Condensed Matter Chemistry

Abstract

Mechanical forces acting on atoms or molecular groups can alter chemical kinetics and decomposition paths. So called mechanochemistry has been proposed to influence a variety of processes, from the formation of prebiotic compounds during planetary collisions to the shock-induced initiation of explosives. It has also been harnessed in various engineering applications such as mechanophores and ball milling in industrial applications. Experimental and computational tools designed to characterize the effect of mechanics on chemistry have focused exclusively on simple linear forces between pairs of atoms or molecular groups. However, the mechanical loading in condensed matter systems is significantly more complex and involves many-body deformations. Therefore, we propose a methodology to characterize the effect of many-body intra-molecular strains on decomposition kinetics and reaction pathways. We combine four-body external potentials with reactive molecular dynamics and show that many body strains that mimic those observed in condensed matter encourage bond rupture in a spiropyran mechanophore and accelerate thermal decomposition of condensed TATB, an energetic material. The approach is generalizable to a variety of systems and can be used in conjunction with ab initio molecular dynamics, and the two examples utilized here illustrates both the versatility of the method and the importance of many-body mechanochemistry.

Extemporaneous Mechanochemistry: Shock-Wave-Induced Ultrafast Chemical Reactions Due to Intramolecular Strain Energy

“…Cluster 6, which is a high temperature, mid-strain state, shows similar results to Cluster 5 with slightly lower counts for the "uncommon" first-step reactions. These agree well with previously reported premeditated TATB mechanochemistry 18 . Overall, we show through large-scale reactive MD simulations a significant acceleration and alteration of reactions in explosive hotspots due to local intramolecular strains that is not accounted for in "traditional" thermal chemistry models.…”

“…These observations agree well with previously reported premeditated TATB mechanochemistry. 18 Overall, we show through large-scale reactive MD simulations a significant acceleration and alteration of reactions in explosive hotspots due to local intramolecular strains that are not accounted for in "traditional" thermal chemistry models. This implies that HE shock initiation is fundamentally an extemporaneous mechanochemical process.…”

“…An unreacted TATB molecule has bonding [18,6,18,6]. When a molecule does not match this pattern for 3 consecutive frames (0.3 ps), we take first frame of the three to be time t1.…”

“…NO2 scission: [<18,6, <18, 6] Ring Fracture: [<18,6,18,6] SM-4: Example molecular structures at characteristic times Example structures at times between t1 and t2 for an intra-molecular hydrogen transfer reaction.SM Figure 1: Structures of a TATB molecule going through an intra-molecular hydrogen transfer reaction. Snapshots show an example molecule at the two characteristic times t1 and t2 defined in the maintext, and at 2.5 ps after these times.…”

Systematic Builder for All‐Atom Simulations of Plastically Bonded Explosives

“…The shock compression of materials can drive a variety of events such as phase transformations [1][2][3], plasticity [4][5][6][7], melting [8,9], intra-molecular deformations [10][11][12], and chemical reactions [13][14][15][16]. Most of these phenomena can be exacerbated by the localization of energy due to the interaction of the shockwaves with the materials microstructure and defects.…”