Long-time structural relaxation of glass-forming liquids: Simple or stretched exponential?

Abstract

This paper presents data for the physical aging of the density of squalane upon both non-linear and nearly linear temperature jumps from states of thermal equilibrium. Invoking the single-parameter-aging scenario [Hecksher et al.,

Theory of the highly viscous flow

“…4 (b). Apart from the starting value 0.58, there is no adapted parameter in the calculated curve, which lies nicely between the cooling and the heating data and corroborates the conclusion [7] that there is a terminal relaxation time (in the present description at 4 √ 2τ c ), even though the relaxation time distribution goes over many decades.…”

“…This is shown in the last example, squalane, in Fig. 4 (a), for the G(ω)-data [40] at 172 K. Since there are also data at 174, 176 and 178 K, one can make a Vogel-Fulcher extrapo-lation to τ c = 188.7 s at 167.73 K, the temperature of a very recent aging experiment [7]. Then one can compare the measured equilibration with the prediction derived from eq.…”

“…A continuity relation between the irreversible and the reversible Kohlrausch relaxation time distribution is derived. The full spectrum can be used in many ways, not only to describe shear relaxation data, but also to relate shear relaxation data to dielectric and bulk relaxation spectra, and to predict aging from shear relaxation data, as demonstrated for a very recent aging experiment [7].…”

“…FIG. 4: (a) Measurement [40] of G(ω) in squalane; theory with G=1.167 GPa, η=0.396 GPas, β = 0.363 and a secondary relaxation gaussian at 0.273 eV with a full width at half maximum of 0.42 eV and the amplitude 0.07 (b) Measured [7] and calculated aging curves in squalane at 167.73 K.…”

Predicting nonlinear physical aging of glasses from equilibrium relaxation via the material time

“…Previously we have worked with this linear limit with temperature jumps down to 100 mK [27][28][29]36]; the data of the present paper takes this a step further by involving temperature jumps as small as 10 mK, as well as by optimizing the protocol to make it possible for the first time properly to resolve both the long-and the short-time plateaus of the linear aging curve. Linearity is investigated by considering the normalized relaxation function of the quantity X, denoted by R X (t), which for a temperature jump at t = 0 is defined by…”