Kovacs effect in PMMA observed by low-frequency Raman scattering (boson peak)

Physical aging and molecular mobility of amorphous polymers

“…This explanation is consistent with the evolution of the boson peak intensity on aging as shown by low frequency Raman scattering (Fig. 2) and inelastic neutron scattering [17,50]. This explanation is also consistent with the energy landscape model [40,52].…”

“…Fig. 6(b) shows the result for an aging temperature T a = 363 K. This experimental investigation shows that the enthalpy decreases drastically when the aging temperature T a is not far below T g , as already observed by Wypych et al [50]. As t a increases, the evolution of the endothermic peak indicates that the final state corresponds to a deeper energy minimum, in direct connection with the slowing down of the dynamics in the glass transition range.…”

Memory effects in the relaxation of the Gaussian trap model

“…This memory effect has not only been observed in the evolution of thermodynamic variables but also shows up in the dielectric constant in both, polymer glasses [8] and a molecular liquid [9]. Furthermore, its occurence is not restricted to the slow time scale of the primary relaxation but it has also been found in the region of the low-frequency vibrations of a glass [10]. The Kovacs effect and its interpretation in terms of simple models has been described in a review-like paper by Bertin et al [11].…”