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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. 

In the region near an interface, the microscopic properties of a glass forming liquid may be perturbed from their equilibrium bulk values. In this work, we probe how the interfacial effects of additive particles dispersed in a matrix can influence the local mobility of the material and its glass transition temperature, T g . Experimental measurements and simulation results indicate that additives, such as nanoparticles, gas molecules, and oligomers, can shift the mobility and T g of a surrounding polymer matrix (even for relatively small concentrations of additive; e.g. , 5–10% by volume) relative to the pure bulk matrix, thus leading to T g enhancement or suppression. Additives thus provide a potential route for modifying the properties of a polymer material without significantly changing its chemical composition. Here we apply the Limited Mobility (LM) model to simulate a matrix containing additive species. We show that both additive concentration, as well as the strength of its very local influence on the surrounding matrix material, will determine whether the T g of the system is raised or lowered, relative to the pure matrix. We demonstrate that incorporation of additives into the simple LM simulation method, which has successfully described the behavior of bulk and thin film glassy solids, leads to direct connections with available experimental and simulation results for a broad range of polymer/additive systems.