Effect of pressure on relaxation dynamics at different time scales in supercooled systems

Abstract

For over 10 decades, the dynamics of two glass-forming systems have been investigated by dielectric spectroscopy under cooling (from melting point to well below the glass transition temperature) and under compression (from atmospheric pressure up to 700 MPa). The α-relaxation time τ_α was significantly affected by both thermodynamic variables, showing equal roles in slowing down the dynamics. Some similarities have been found; for instance, the dispersion of the α-process was shown to increase with decreasing temperature T and increasing pressure P. Furthermore, the same shape for relaxation dynamics over a broad time-scale was found by comparing two dielectric loss spectra obtained at different T and P but characterized by the same τ_α(T, P). Additionally, it is noteworthy that the effect of T and P on slowing down the time scale of fast relaxation processes (β-relaxation and excess wing), although less strong than in the case of α-process, was again comparable. The evidence demonstrates that in the investigated systems: (a) slow and fast relaxations are strongly related; (b) the shape of α-relaxation and (c) the separation between α- and β-relaxation time scale are controlled by τ_α(T, P) and not by separate thermodynamic variables.

Acknowledgment

The authors thank ‘Nanopack’ FIRB 2003 D. D. 2186 grant RBNE03R78E for financial support.