A New Approach to the Glass Transition of Percolated Polymers from the Perspective of Thermal Volume Expansion

Abstract

In 1995, the Nobel Price winner P.W. Anderson made the following remarkable statement: The deepest and most interesting unsolved problem in solid state theory is probably the theory of the nature of glass and glass transition. Although there have been new theoretical developments in the meantime, in our opinion, this situation has only improved marginally to date. One of the main reasons is the insufficient consideration of experimental boundary conditions. A central experimental problem arises from the fact that the time constants required to achieve thermodynamic equilibrium increase sharply in the vicinity of and above a hypothetical static glass transition. If these equilibrium conditions are violated, additional internal thermodynamic variables come into play that normally alter the static and dynamic susceptibilities significantly and thus lead to misinterpretations of the experimental data. This raises, for example, the question of whether there are static property changes during the canonical glass transition and how these correlate with dynamic precursors. In this article, we attempt to find answers to these questions using a new experimental method called temperature-modulated optical refractometry in combination with the temperature-jump technique. The total time required to investigate the glass transition behaviour of our model epoxy was approximately two years.