Prof. Wang Junqiang’s team at the Ningbo Institute of Materials Technology and Engineering (NIMTE) of the Chinese Academy of Sciences (CAS), has revealed that the exponential relaxation events during the recovery process of glasses, providing a solid evidence that non-exponential relaxation peaks in glasses are composed of series of exponential relaxation units. The study was published in Proceedings of the National Academy of Sciences (PNAS).
Nonexponential relaxation reflects the nature of glasses, which is among the research hotspots in condensed matter physics. A hypothesis that nonexponential relaxation peaks include a series of exponential events is well-known, but has not been verified. It can be attributed to the lack of critical experimental evidence, especially a systematic exponential relaxation spectrum in glasses.
To address this issue, researchers at NIMTE have delved into the exponential relaxation spectrum in glasses during the recovery process.
The enthalpy relaxation peaks after annealing treatment were measured by virtue of a high-precision nanocalorimetry, which is universal for metallic glasses and organic glasses. To compare the enthalpy relaxation spectrum, the dynamic mechanical spectra were measured under sinusoidal tensile stress via a dynamic mechanical analyzer (DMA).
The relaxation peaks exhibited exponential characters, which can be fitted by the Debye function. The exponential relaxation events are the units of relaxations in glasses. It is termed as Relaxun, as the abbreviation of relaxation unit. Besides, the activation energy of relaxation spectrum under different annealing temperature and annealing time was determined.
A complete spectrum of the exponential relaxation peaks was obtained over a wide temperature range from 0.63Tg to 1.03Tg, which was similar with the DMA loss modulus curve, thus reflecting that the non-exponential relaxation peaks can be divided into exponential relaxation units. In other words, the spectrum can be controlled by multi-step annealing treatment precisely.
The activation energy covers a wide range from α relaxation to β relaxation and even the fast γ/β′ relaxation. Furthermore, the quantitative contributions of different relaxation modes to the nonequilibrium enthalpy evolution during aging were measured.
This work can shed light on the non-equilibrium thermodynamics research as well as the precise glass property modulation through the relaxation mode control.
Fig. The spectrum of the exponential relaxation peaks (Image by NIMTE)
Contact
WANG Junqiang
Ningbo Institute of Materials Technology and Engineering
Email: jqwang@nimte.ac.cn