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

Abstract

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 (Tg) than the glass formed under ambient pressure. The sensitivity parameter of Tg 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 Tg upon compression. The origin of the hypersensitivity of Tg to pressure history was revealed by structural analyses, positron annihilation lifetime spectroscopy, and molecular dynamics …