The caged dynamics, the Johari-Goldstein β relaxation, and the structural α-relaxation and their interconnections in...

The presence of caged dynamics, the Johari-Goldstein (JGβ) relaxation preceding the cooperative α-relaxation, and the fact that their properties are interconnected have been established universally for glass-forming liquids of various kinds [K. L. Ngai, Prog. Mater. Sci. 139, 101130 (2023)]. We apply the universal properties of the three processes in interpreting or reinterpreting the calorimetric and dielectric relaxation data of four amorphous waters: amorphous solid water (ASW), hyperquenched glassy water (HGW), low-density liquid water (LDL), and high-density liquid water (HDL). The presence of the JGβ relaxation and the caged dynamics before the terminal α-relaxation, and the interrelations between their respective properties, are found in the four amorphous waters exactly as in other glass-formers. The existence of the JGβ glass transition temperature, Tgβ, is found indirectly from the response of the caged dynamics in ASW, HGW, and HDL, and its value of ∼113 K is consistent with the extrapolation of the dielectric JGβ relaxation times τβ(T) to long times. The calorimetric data of LDL at a heating rate of 10 K/min show Tgα of LDL is 136 K, which is the same as that of ASW and HGW incidentally. The calorimetric and dielectric data of HDL at temperatures below 125 K, before it transforms to LDL at higher temperatures, are interpreted as originating from the JGβ relaxation and not from the α-relaxation. The value of Tgβ of HDL obtained from calorimetry or deduced from the dielectric JGβ relaxation times τβ(T) is also near 113 K. The α-relaxation glass transition temperature Tgα of HDL, obtained by extrapolating the values from calorimetric and volumetric studies at elevated pressure to ambient pressure, are 137 and 128 K respectively. The 137 K for Tgα is supported by observation of glass transition at the same temperature by DSC in samples of HDL prepared by compressing droplets of HGW. Assuming τα(Tgα) is 100 s, the value of the calorimetric Tgα for HDL is close to the calorimetric and dielectric τα(T) of HGW. The τα(T) of HGW and LDL have Arrhenius temperature dependence with a small fragility index m. The Arrhenius temperature dependence of τβ(T) for HGW, HDL, and LDL are similar as well. Applying the relation between τα(T) and τβ(T) from the Coupling Model, the averaged coupling parameter nav ∼ 0.18 is deduced for all four amorphous waters. Such a small value of nav is consistent with the frequency dependence, ∼ν-nav, on the high-frequency flank of the α-loss peak of HGW and LDL Thus, the small nav correlates with the small m, in accord with the correlation found in other glass-formers.