Progress on Terahertz Spectroscopy Detection of Glass Transition of Polymers

The polymer glass transition, as a transition between the glassy and highly elastic states of amorphous polymers, has an important impact on material properties, especially mechanical properties. Terahertz spectroscopy, as a novel spectroscopic analysis technique with the advantages of non-contact, rapidity, and high sensitivity, shows important potential for application in polymer glass transition studies. By summarizing and analyzing the findings in the literature in the last 15 years, this paper aims to provide a comprehensive understanding of the current status of the application of terahertz spectroscopy in this field and to look forward to its future development. Firstly, the properties of the polymer glass transition are introduced, and traditional measurement methods and the limitations they face, such as thermal analysis, dynamic mechanical analysis, and infrared spectroscopy, are explored. Researchers have begun to look for new study methods to compensate for these limitations. Terahertz spectroscopy can provide both spectral and phase information, allowing direct measurement of refractive index and dielectric constant and reflecting the free volume change of the polymer chain, which is why the THz spectroscopy can detect the glass transition of polymers. Subsequently, the progress in applying terahertz spectroscopy in studying polymer glass transition in recent years is summarized. Results of these studies show that terahertz spectroscopy can accurately determine the glass transition temperatures, provide microscopic information about the structure and conformation, and reveal the glass transition mechanism and dynamics behavior of polymers, including poly formaldehyde, polyamide, poly (epsilon-caprolactone), and polylactic acid. Moreover, this paper points out the existing problems of terahertz spectroscopy, including the bandwidth limitations and high cost of terahertz spectrometers. Therefore, future research needs further to improve the performance of terahertz sources and instruments, develop more efficient data analysis methods, and explore the potential of terahertz spectroscopy for industrial applications. Overall, terahertz spectroscopy, as an emerging research tool, has made positive advances in the field of polymer glass transition and can enable rapid and sensitive detection of polymers as well as precise structural analysis.