Breaking Bonds by Mechanical Stress:  When Do Electrons Decide for the Other Side?

Abstract

Using first-principles molecular dynamics, we have simulated reactions that can be induced by mechanical stress in a polymer. We have stretched a small piece of poly(ethylene glycol) (PEG) in water at finite temperature. Both the molecule and the solvent were described quantum mechanically on an equal level. The formation of ions was observed, which corresponds to a heterolytic bond cleavage. We were able to monitor the motion of the electrons during the reactions. Our simulations show that the electron transfer and the breaking of the bond occur almost simultaneously and that both processes are initiated by the approach of a solvent molecule toward the destabilized bond.

Mechanically activated rupture of single covalent bonds: evidence of force induced bond hydrolysis

“…23,24 As pointed out in previous studies, 14,18 small microruptures, which are frequently observed in the force-distance curves of the amino-linked CMA, clearly indicate that a bond within the surface linker is indeed breaking in this experimental system. Within this surface linker, the carboxylic acid amide bond (C(O)-N), and the siloxane bond (Si-O) are both hydrolysable in aqueous environments.…”

Squeezing out hydrated protons: low-frictional-energy triboelectric insulator charging on a microscopic scale

“…113 It is also conceivable that mechanical forces may increase the dissociation rate of adsorbed water by disconnecting hydrogen bonds of, e.g., the autodissociation transition states of water, which under normal conditions in most cases does not separate into two water ions. 116 Simulations have also indicated that adsorbed water may enhance the heterolytic mechanical breaking of chemical bonds, 117 and it has been suggested that adsorbed water molecules may be decomposed tribochemically into hydrogen radicals and a hydroxyl anions by emitted triboelectrons. 109 A quantification of these mechanisms would be important for differentiating between water-based versus water-enhanced charging mechanisms.…”

Theoretical Approaches for Understanding the Interplay Between Stress and Chemical Reactivity

“…During these simulations, F is applied by increasing the distance between a pair of atoms at a constant velocity. They have used this approach to explore the changes in electronic structure that occur when solvated polymers are stretched to the point of rupture [41]. Their studies showed that bond rupture occurred through a heterolytic process involving solvent molecules.…”

“…These studies have focused primarily on simulating molecular systems exposed to external forces by treating the system as though it moves on a force-modified potential energy surface that incorporates the work performed on a chemical system as it undergoes structural changes in the presence of an external force. These studies have examined the rupture forces of bonds [32], the reactivities of molecules subjected to tensile stresses and strains [38][39][40][41], the effects of strains on pericyclic reactions [14, 29-31, 33, 34, 42-44], the differences between thermochemistry and mechanochemistry [45], and the effects of chain length on the transduction of external forces at atomic levels [46,47].…”