On the fragility of complex material systems

Abstract

In this work we investigate, from both a macroscopic and a microscopic point of view, the fragility degree of complex material systems. In particular, we integrate a microscopic and a macroscopic approach. The former is formulated in the framework of non-equilibrium thermodynamics in order to obtain the phenomenological equations for the heat flux and viscous pressure tensor, as functions of the absolute temperature T and of the small strain tensor, in the isotropic case, where the shear viscosity is supposed to depend on Tg/T. The latter is connected with a macroscopic definition of fragility, operatively introduced by Angell for glass-forming systems, and with the definition of thermal restraint, based on elastic incoherent neutron scattering data. On that score literature data of viscosity, as a function of concentration and temperature, and literature data of elastic intensity data are correlated with the system fragility and with the system thermal restraint. The obtained results are of interest for a wide range of innovative materials, such as, for example, carbon nanotubes and bioprotectant systems.