Effect of combined pressure and temperature changes on structural recovery of glass‐forming materials. I. Extension of the KAHR model

Abstract

The KAHR model of structural relaxation has been extended to include the effects of pressure upon the retardation times of glass‐forming materials. The previously used methodology is applied with a continuous distribution of retardation times of the fractional exponential form. Several forms of the pressure dependence are examined. The combined temperature and pressure changes on structural recovery of glasses are addressed in this paper.

Isobaric and isothermal glass transition of PMMA: pressure-volume-temperature experiments and modelling predictions

“…The equation that describes the volume relaxation kinetics in the presence of an arbitrary temperature and pressure history reads [10][11][12][13][14]:…”

“…(1) and gives a good description of experimental data over a broad dynamic range [6,7,9]. In literature two main phenomenological models have been utilized in order to predict the behaviour of glass forming materials, namely the Kalroush, Aklonis, Hutchinson, and Ramos (KAHR) model [10,11] and the Tool-Narayanaswamy-Moynihan (TNM) model [15][16][17]. These theories are both capable of capturing the nonlinearity and memory effect of structural relaxation.…”

A Measuring System for Bulk and Shear Characterization of Polymers

“…The time-dependent changes of specimen geometry caused by temperature jumps are commonly known as physical aging [1,2,9], and are relatively well understood. Much less is known about the effect of pressure variations [10,11]. The quantitative interrelation between the effect of temperature and the effect of pressure is essentially not known.…”

“…The bulk creep compliance, B(t), essentially represents the effect of pressure-induced physical ageing at small pressure jumps [1,[9][10][11]. Using the isothermal segments of B(t), shown in Fig.…”

Structural relaxation in the glass: Evidence for a path dependence of the relaxation time

“…s is known as the characteristic relaxation time (although it is actually a retardation time), and b is the non-exponentiality or stretching parameter. Various phenomenological equations have been used to describe the dependence of the characteristic relaxation time s on temperature and structure and sometimes pressure, including the TNM equation [22], equations derived by Hodge [40] and Scherer [41], both based on the approach of Adam and Gibbs [42], the KAHR and similar equations [23,43] based on free volume, and several others [33,44]. The most widely used forms are the TNM [22] and KAHR [23] equations for isobaric structural recovery; the KAHR equation is written in terms of d, whereas the TNM equation is written in terms of T f :…”