Modeling the Depth-dependent Dynamics of Confined Systems

This talk will focus on our recent results modeling dynamics and glassiness in confined systems. One technique is the Limited Mobility model (LM), a coarse-grained kinetic simulation approach where mobility at a site depends on facilitation through mobility at nearby sites. LM results include mobile layer depths in freestanding films, as well as the effect of nanoparticles on the surrounding matrix. Our Cooperative Free Volume model (CFV) is a different approach. This is a rate model in which the system's free volume (V_free), predicted through our Locally Correlated Lattice (LCL) equation of state analysis of bulk thermodynamic data, plays the key role in determining the local molecular cooperativity. The CFV model describes independent T- and V_free - contributions to the pressure-dependent segmental relaxation times, tau(T,V). This talk will focus on our ability to describe the dynamics of confined systems, where the local density (and thus the V_free-contribution) is altered by the presence of an interface. For example, our recent CFV work reveals the point at which film samples lose the contribution from regions of bulk-like dynamics, which will lead to insight on the position-dependent mobility across an interfacial region.