Modeling Glass-Forming Systems to Illuminate Connections Between Experimental Properties

In this talk we will discuss our recent work in the modeling of dielectric spectroscopy data on glass-forming polymers, nanocomposites, and interfaces, as well as our current research on rheological properties, ellipsometry of polymer films to obtain free volume, and expansivities of melts and glasses under mechanical constraint. The thread that ties together all of these projects is our goal to relate thermodynamic concepts like expansivity, random close-packing, and free volume to dynamics measurements such as segmental relaxation times (τ) and glass transition temperatures (T_g). Our modeling begins with analysis of thermodynamic data (e.g. PVT data) to reveal the system's characteristic volume at random close-packing (V_cp), from which free volume, V_free(T,P) = V(T,P) − V_cp, can be defined. This definition is fundamental and can be unambiguously applied; it does not a priori assume a connection to dynamics and does not require any dynamics data, yet, it correlates strongly with T_g and τ. For example, knowledge of V_free(T,P) allows us to predict the volume-based contribution to dynamics, because of the general form lnτ(T,P) ∼ f(T)×(1/V_free(T,P)) resulting from our model for segmental relaxation.