On the isothermal pressure behaviour of the relaxation times for supercooled glass-forming liquids

Abstract

This paper discusses the isothermal pressure behaviour of the relaxation times for supercooled glass-forming liquids. Analysis based on reference data and the authors' measurements of dielectric relaxation is carried out for both strong and fragile glass formers. All of the experimental relaxation times clearly exhibit a non-Arrhenius behaviour well reproduced by a function τ = τ 0p exp(C p P /(P 0 − P )) or τ = τ 0 exp(CP 0 /(P 0 − P )), giving the same estimates of the ideal glass transition pressure P 0 . Experimental data indicate that fragile materials show a more rapid increase of the relaxation time with rise of pressure than the strong ones.

Effect of Temperature and Pressure on Segmental Relaxation in Polymethylphenylsiloxane

“…There have been various equations proposed to describe the pressure dependence of τ. [23][24][25][26][27] Substituting P -1 for T in Equation 1, a pressure variant of the Vogel-Fulcher equation can be obtained 23,28 (3)…”

New Challenges for the Pressure Evolution of the Glass Temperature

“…2 can reliably portray experimental data only for "strong" (weakly non-Arrhenius) glass formers, assuming that measurements terminates at P max ≪ P 0 . In Paluch et al (1998), the relation able to portray the previtreous dynamics for an arbitrary glass former and range of pressure was proposed:…”

On the pressure evolution of dynamic properties of supercooled liquids

“…However, in 1998 it was noted that it can yield a reliable parameterization only for fragile glass formers [7]. Consequently, a new pressure counterpart of the VFT relation (referred to herein as the PVFT), which introduced the pressure fragility strength coefficient D P , was proposed [7]:…”

“…However, for the PVFT equation (5) the prefactor τ P 0 is linked to the relaxation time at the atmospheric pressure, or any pressure P > 0.1 MPa at which measurements started for a given isotherm. Consequently, it can take on arbitrary values ranging from picoseconds to even seconds [4,5,7,[9][10][11][12][13][14].…”

“…Similar dependences can be written for the dielectric (structural) relaxation time τ (T ), viscosity η(T ), DC conductivity σ (T ), and diffusion coefficient d(T ) [1,[4][5][6][7][8][9][10].…”