Connecting Pressure-Dependent Dynamics to Dynamics under Confinement: The Cooperative Free Volume Model Applied to Poly(4-chlorostyrene) Bulk and Thin Films

Abstract

We apply our cooperative free volume (CFV) rate model for pressure-dependent dynamics to describe the relaxation times for poly(4-chlorostyrene) (P4ClS) bulk and thin films. The CFV model expresses segmental relaxation times, τ, as a function of temperature, T, and thermodynamic free volume, Vfree = V – Vhc, where the limiting hard core volume, Vhc, is obtained via analysis of a polymer’s experimental PVT data using the locally correlated lattice (LCL) model equation of state. In adapting CFV to describe thin films, we assume that the main effect of confinement is that the interface serves to change the average free volume (average density) compared to bulk. We formulate a simple weighted average expression (involving just a single interface related parameter) to describe the free volume of a film as a function of thickness, h, and use this h-dependent Vfree within the CFV model expression. Using just ambient pressure relaxation time data on bulk P4ClS, along with PVT data, we parametrize the CFV model, w...