Building on the WLF/free volume framework: Utilization of the coupling model in the relaxation dynamics of the gelatin/cosolute system

Abstract

The onset of softening in the glass transition dispersion of the gelatin/ cosolute system at 78% solids was examined using the stress relaxation modulus and dynamic oscillatory data on shear. Measurements were made between 5 and -70 °C, and isothermal runs were reduced to a master curve covering 21 orders of magnitude in the time domain. The sharpness with which the mechanical properties of our system changed with temperature was reflected in the shift factor aT used to pinpoint the glass transition temperature (Tg). The prevalent analytical framework traditionally employed to follow the transition from the rubbery to glasslike consistency in biomaterials is that of the free volume theory in conjunction with the WLF equation. Increasingly, the combined WLF/ free volume approach is challenged by the coupling model, which is able to provide additional insights into the physics of intermolecular interactions in synthetic materials at the vicinity of Tg. The model in the form of the Kohlrausch-Williams-Watts function described well the spectral shape of the local segmental motions of gelatin/cosolute at Tg. The analysis provided the intermolecular interaction constant and apparent relaxation time, parameters which depend on chemical structure. Results appear to be encouraging for further explorations of the dynamics of densely packed biomaterials at the glass transition region. © 2006 American Chemical Society.