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Crucial data for modelling dynamics and miscibility are reflected in thermal expansivities. Analysis of ten polymer films and correlation with volumetric data show ellipsometry is an effective route. 

In this paper we model the segmental relaxation in poly(2-chlorostyrene) 18 nm freestanding films, using only data on bulk samples to characterize the system, and predict film relaxation times ( τ ) as a function of temperature that are in semi-quantitative agreement with film data. The ability to translate bulk characterization into film predictions is a direct result of our previous work connecting the effects of free surfaces in films with those of changing pressure in the bulk. Our approach combines the Locally Correlated Lattice (LCL) equation of state for prediction of free volume values ( V free ) at any given density ( ρ ), which are then used in the Cooperative Free Volume (CFV) rate model to predict τ ( T , V free ). A key feature of this work is that we calculate the locally averaged density profile as a function of distance from the surface, ρ av ( z ), using the CFV-predicted lengthscale, L coop ( z ), over which rearranging molecular segments cooperate. As we have shown in the past, ρ av ( z ) is significantly broader than the localized profile, ρ ( z ), which translates into a relaxation profile, τ ( z ), exhibiting a breadth that mirrors experimental and simulated results. In addition, we discuss the importance of averaging the log of position dependent relaxation times across a film sample (〈log  τ ( z )〉), as opposed to averaging the relaxation times, themselves, in order to best approximate a whole sample-averaged value that can be directly compared to experiment. 

ABSTRACT We apply the cooperative free volume (CFV) rate model for pressure-dependent dynamics of glass-forming liquids and polymer melts, focusing on two new applications of the model, to natural rubber and to polyurea. In CFV, segmental relaxation times, τ, are analyzed as a function of temperature (T) and free volume (Vfree), where the latter provides an insightful route to expressing dynamics relative to using the system's overall total volume (V). Vfree is defined as the difference between the total volume and the volume at close packing and is predicted independently of the dynamics for any temperature and pressure using the locally correlated lattice equation-of-state analysis of characteristic thermodynamic data. The new results for natural rubber and polyurea are discussed in the context of results on a set of polymeric and small-molecule glass formers that had previously been modeled with CFV. We also discuss the results in the context of recent connections that we have made with the density-scaling approach.