One of the most notable deviations from bulk fluid properties is the onset of a thickness-dependent glass transition temperature (T g ) for nanometrically thin polymer films. Experimental and theoretical observations suggest that this behavior is a response to the interfaces, which perturb the local properties of a film and play an increasingly important role in influencing the global properties of a film as its thickness decreases. In this work, we probe the global and local properties of free-standing films using our limited mobility (LM) model, which is a simple kinetic lattice model that simulates free volume and mobility in a fluid. We provide insight about the role of mobility in affecting the thicknessdependent film-average T g of free-standing polymer films by characterizing the depth to which mobility propagates from a free surface, i.e., the "mobile layer depth". We also consider the effect of "stacking" free-standing polymer films, where confinement by interfaces composed of the same material yields T g suppression intermediate to that of substrate supported and free-standing films. In order to characterize the local properties of a film, we utilize "reporting layers" located near the free surface and film interior, from which we compute local glass transition temperatures and make connections with experimental results reported for real polymer films.

In this article, we connect the experimental miscibility of several polymer/supercritical carbon dioxide (scCO 2 ) mixtures with their pure component properties, such as free volume and interaction energy. We directly address the experimental observations that suggest free volume-rich polymers and those with weak polymer segment−segment interaction energies mix more favorably with scCO 2 . By applying our simple locally correlated lattice (LCL) theory to model the pressure−volume−temperature (PVT) behavior of the pure polymers and supercritical solvent, we obtain characteristic molecular parameters which are then used to predict the key physical properties of interest. We probe the underlying thermodynamic contributions (entropic and enthalpic) to the free energies of mixing and show that our LCL theory can explain the experimental miscibility ranking based solely on our characterization of the pure components.

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...

Alternative perspectives of mobility method 1 (blue) vs. method 2 (red) compared to experimental data (symbols).