Volume and Enthalpy Relaxation in Polystyrene

Anomalous Enthalpy Relaxation in Vitreous Silica

It is a challenge to calorimetrically determine the glass transition temperature (Tg) of vitreous silica. Here, we demonstrate that this challenge mainly arises from the extremely high sensitivity of the Tg to the hydroxyl content, but also from decrease of the Tg with repeating the calorimetric scans. It is known that the liquid fragility (i.e., the speed of the viscous slow-down of a supercoo...

enthalpy relaxation of gelatin in the glassy state

the glass transition temperature (tg) and the melting temperature (tm) of gelatin at water contents between 7 and 14% were measured using differential scanning calorimetry.  the plasticisation of the polymer by water led to a decrease in tg and tm. the tg of partially crystalline gelatin was higher than that of the amorphous one obtained by quenching from the melt. the enthalpy relaxation occur...

Thermodynamics of Enthalpy Relaxation and Hole Formation of Polymer Glasses

Relaxation of a rubbed polystyrene surface.

The relaxation dynamics of a rubbed polystyrene (PS) surface have been characterized using infrared-visible sum frequency generation spectroscopy (SFG). The SFG results were compared with previous relaxation of retardation measurements, and the results show that the rubbed PS surface has the same T(g) as the bulk where T(g) is defined as tau(T(g))=5 s, however, the surface has a lower activatio...

Adam-Gibbs Formulation of Enthalpy Relaxation Near the Glass Transition

The entropically based nonlinear Adam-Gibbs equation is discussed in the context of phenomenologies for nonlinear enthalpy relaxation within the glass transition temperature range. In many materials for which adequate data are available, the nonlinear Adam-Gibbs parameters are physically reasonable and agree with those obtained from linear relaxation data and thermodynamic extrapolations. Obser...