Hypersensitivity of the Glass Transition to Pressure History in a Metal-Organic Framework Glass

Metal-organic framework (MOF) glasses feature numerous unique properties and potential applications, but many fundamental questions remain unanswered, especially concerning their glass transition. Here, we report a discovery about ZIF-62 glass (a typical MOF glass), namely, the hypersensitivity of its glass transition to pressure history. Specifically, upon quenching the ZIF-62 melt under a modest pressure of 60 MPa, the derived glass exhibited a significantly lower glass transition temperature (T-g) than the glass formed under ambient pressure. The sensitivity parameter of T-g to pressure for ZIF-62 glass is much higher than that of other glass systems, including polymer glasses that typically feature a huge increase in T-g upon compression. The origin of the hypersensitivity of T-g to pressure history was revealed by structural analyses, positron annihilation lifetime spectroscopy, and molecular dynamics simulations. We found that the medium-range structure change induced the drop in T-g.

Automated summary

A recent study has found that certain metal-organic framework (MOF) glasses exhibit hypersensitivity of their glass transition temperature (T-g) to pressure history, with a much higher sensitivity parameter compared to other glass systems. The hypersensitivity was found to be caused by changes in the medium-range structure.