Universal Features of Manifestation of Relationship between Local and Segmental Dynamics of Glassy Polymers at Terahertz Frequencies in IR Spectra

Abstract

Temperature dependences of low-frequency IR spectra of glassy polymers are studied in the range of ν = 0.24–4 THz (8–135 cm^–1) at temperatures from 90 to 400 K. Analysis of these dependences revealed absorption corresponding both to individual and correlated torsional vibrations, which initiate the relaxation dynamics. The temperature evolution of the IR spectra in the range of terahertz frequencies exhibits three universal behaviors, namely, the low-temperature regime corresponding to the anharmonicity of torsional vibrational motions, the high-temperature regime caused by the contribution of α relaxation (glass formation), and the intermediate stage related to the activation of the conformational mobility of chains due to the β transition. The results obtained are applicable to polymers with both hydrogen and van der Waals bonds between macromolecules.