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

The glass transition temperature (T_g) 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 T_g. Fluorescence spectroscopy is used to measure the glass transition temperature (T_g) of the ultrathin dye-labeled PS layers at specific regions within multilayer films of immiscible polymers. The T_g 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 T_g 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 Macromolecules 2012, 45, 8319] with the same neighboring polymer, which indicates a common physical origin of T_g perturbations in both systems. The magnitude of T_g-confinement effects depends not only on the T_g 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.