Small activation entropy bestows high-stability of nanoconfined D-mannitol* *Project supported by the National Natural Science Foundation of China (Grant Nos. 52001319, 52071327, 51922102, 51771216, and 51701230), the Natural Science Foundation of Zhejiang Province, China (Grant Nos. LR18E010002), the Ningbo 2025 Science and Technology Innovation Project (Grant No. 2019B10051), and the Natural Science Foundation of Ningbo City (Grant No. 202003N4354).

Abstract

It has been a long-standing puzzling problem that some glasses exhibit higher glass transition temperatures (denoting high stability) but lower activation energy for relaxations (denoting low stability). In this paper, the relaxation kinetics of the nanoconfined D-mannitol (DM) glass was studied systematically using a high-precision and high-rate nanocalorimeter. The nanoconfined DM exhibits enhanced thermal stability compared to the free DM. For example, the critical cooling rate for glass formation decreases from 200 K/s to below 1 K/s; the T g increases by about 20 K–50 K. The relaxation kinetics is analyzed based on the absolute reaction rate theory. It is found that, even though the activation energy E* decreases, the activation entropy S* decreases much more for the nanoconfined glass that yields a large activation free energy G* and higher thermal stability. These results suggest that the activation entropy may provide new insights in understanding the abnormal kinetics of nanoconfined glassy systems.