Viscosity, relaxation time, glass temperature, melting temperature and fragile-to-strong transition parameterizations at extreme pressures in soft-matter systems

Abstract

This contribution presents the extended, pressure-related Vogel–Fulcher–Tammann equation applied to portray the pressure evolution of viscosity η (P) and the related dynamic properties, such as the primary relaxation time τ (P), in soft-matter systems as well as the modified Simon–Glatzel-type equation for describing pressure dependences of the glass temperature T _g (P), the melting temperature T _m (P) and the fragile-to-strong dynamical transition in confined water T _d (P). Both equations are capable of penetrating the negative pressure (isotropically stretched liquid) domain, and at very high pressures are capable of the inverse behavior. They have the following forms: (i) η (P)=η₀ exp [D _P Δ P/(P ₀−P)]=η₀ exp [(D _P P−D _P P _SL)/(P ₀−P)], where P ₀ is the estimate of the ideal glass temperature, P _SL is for the stability limit at negative pressures and D _P denotes the pressure fragility strength coefficient and (ii) , where and are the reference temperature and pressure,−π is the negative pressure asymptote and c is the damping coefficient responsible for the inversion phenomenon.

Keywords:

• glass temperature
• dynamics
• relaxation time
• viscosity
• pressure

Acknowledgement

This work was supported by Ministry of Science and Education (Poland), grant N202 231737.