Role of neighboring domains in determining the magnitude and direction of Tg-confinement effects in binary, immiscible polymer systems

Abstract

The glass transition temperature (Tg) of a polystyrene (PS) nanolayer is shown to be strongly tuned by the presence of neighboring immiscible polymer layers over a 100 °C range spanning temperatures above and below the bulk PS Tg. Fluorescence spectroscopy is used to measure the glass transition temperature (Tg) of the ultrathin dye-labeled PS layers at specific regions within multilayer films of immiscible polymers. The Tg of a 14-nm-thick PS layer is 45 °C atop poly(n-butyl methacrylate) and 144 °C atop poly(4-vinyl pyridine). Additionally, the Tg of an 11- to 14-nm thick PS layer is shown to be the same as that reported by a near-infinitely-dilute PS blend component [Evans and Torkelson Macromolecules2012, 45, 8319] with the same neighboring polymer, which indicates a common physical origin of Tg perturbations in both systems. The magnitude of Tg-confinement effects depends not only on the Tg of the neighboring domain but is also strongly correlated with neighboring domain fragility, a fundamental property of glass formers which provides a link between medium-range structural order and dynamics.