It’s possible to initiate chemical reactions using mechanical forces such as extreme pressure or shear. Early investigations of this “mechanochemistry” suggested that, sometimes, the application of pressure and shear could lead to rheological explosions or detonations in otherwise inert substances such as sucrose. An article in the Journal of Applied Physics reports changes in vibrational and Raman spectra during the application of simultaneous pressure and shear to sucrose, and evidence for both a phase transition and subsequent decomposition of the high-pressure phase.

The authors used a rotational diamond anvil cell to combine pressure and shear forces. The sucrose was placed in a sample compartment created from a stainless steel gasket indented to a thickness of 75 micrometers, and with a sample well 160 micrometers in diameter. Helium, pumped into the diamond anvil cell, served as a pressure-transmission medium while shear was generated by rotating one anvil with respect to the other. They used a home-built instrument to measure Raman spectra that included a laser diode pumped solid-state laser with an operating wavelength of 532 nm. They also took Synchrotron IR measurements using a beamline at the Brookhaven National Laboratory.

A phase transition from Phase I to II was confirmed when the applied pressure exceeded 5 gigapascals. The researchers observed a significant molecular deformation when shear forces were applied to the high-pressure form of sucrose, Phase II. This exotic form of sucrose exhibits unusual bifurcated, three-center hydrogen bonds, normally found only in active biological substances. Although no direct evidence of detonation was observed in these experiments, a brown tarlike substance was recovered after quenching, indicating that some decomposition of Phase II sucrose does occur under these extreme conditions.

Source: “Mechanochemical induced structural changes in sucrose using the rotational diamond anvil cell,” by Jennifer A. Ciezak-Jenkins and Timothy A. Jenkins, Journal of Applied Physics (2018). The article can be accessed at https://doi.org/10.1063/1.5020231.