To Understand Film Dynamics Look to the Bulk*

In recently published work¹ we show that shifts in dynamics of confined systems relative to that of the bulk material originate in the properties of bulk, and exhibit the same form of behavior as when different bulk isobars are compared. By applying our Cooperative Free Volume (CFV) model, employing the Locally Correlated Lattice (LCL) equation of state, we connect in a formal and quantitative way the impact of sample nanoconfinement on segmental dynamics to the effect of changing the thermodynamic state of a bulk sample. This analysis succeeds because control of temperature and control of density in altering dynamic response are multiplicatively linked. The result is that our model leads to predictive power: characterization of bulk behavior allows us to anticipate how changing pressure and/or film thickness will affect sample free volume, local activation energies, and cooperativity requirements. This talk will provide a clear presentation of the above, and show how the work leads to a deeper understanding of what drives segmental relaxation under a wide variety of sample conditions. 1. White, R.P.; Lipson, J.E.G. Physical Review Letters (2020) 125, 058002.