(248d) Direct Measurement of the Local Glass Transition in Diblock Copolymers and Nanocomposites

Nanoscale compositional heterogeneity in block copolymers can impart synergistic property combinations, such as stiff ness and toughness. However, until now, there has been no experimental method to locally probe the glassy dynamics at a specific location within these structured materials. Here, this was achieved by incorporating pyrene-bearing monomers at specific locations along the polymer chain, allowing the labeled monomers local environment to be interrogated via fluorescence. We show that in lamellar forming poly(butyl methacrylate-b -methyl methacrylate) diblock copolymers, a strong gradient in glass transition temperature, Tg, was mapped with nanometer resolution. These measurements also revealed a strongly asymmetric influence of the domain interface on Tg, with a much smaller dynamic gradient being observed for the lower-Tg block. Finally, we also how fluorescence can be used to isolate the effects of irreversible adsorption on the local T_gin polymer nanocomposites. We show that in silica-polystyrene nanocomposites, interfacial adsorption has a strong influence on the local T_gand that the effects strongly depend on the annealing conditions. By comparison of local and bulk properties, we provide new insights into how this phenomenon can be exploited to control nanocomposite properties.