Department of Chemistry and Bioscience, Aalborg University, Aalborg DK-9220, Denmark.
Phys Chem Chem Phys. 2018 Jul 11;20(27):18291-18296. doi: 10.1039/c8cp02340a.
In this work, we explore the thermodynamic evolution in a melt-quenched metal-organic framework glass, formed from ZIF-62 upon heating to the melting point (Tm), and subsequent enthalpy relaxation. The temperature dependence of the difference in Gibbs free energy between the liquid and crystal states of ZIF-62 in the temperature range from the glass transition temperature (Tg) to Tm is found to be weaker than those of other types of glasses, e.g., metallic glasses. Additionally, we find that the stretched exponent of the enthalpy relaxation function in the glass varies significantly (β = 0.44-0.76) upon changing the extent of sub-Tg annealing, compared to metallic and oxide glasses with similar Tgs, suggesting a high degree of structural heterogeneity. Pair distribution function results suggest no significant structural changes during the sub-Tg relaxation in ZIF-62 glass.
在这项工作中，我们研究了熔融金属-有机骨架玻璃中热力学的演变，该玻璃由 ZIF-62 在加热到熔点（Tm）以及随后的焓弛豫过程中形成。我们发现，在玻璃化转变温度（Tg）到 Tm 的温度范围内，ZIF-62 的液态和晶态之间的吉布斯自由能差的温度依赖性比其他类型的玻璃（例如金属玻璃）弱。此外，我们发现，与具有相似 Tg 的金属和氧化物玻璃相比，在亚 Tg 退火程度发生变化时，焓弛豫函数的拉伸指数（β=0.44-0.76）有显著变化，这表明结构具有高度的异质性。配分函数结果表明，在 ZIF-62 玻璃的亚 Tg 弛豫过程中没有发生明显的结构变化。
