Direct Measurement of the Local Glass Transition in Self-Assembled Copolymers with Nanometer Resolution

Abstract

Nanoscale compositional heterogeneity in block copolymers can impart synergistic property combinations, such as stiffness and toughness. However, until now, there has been no experimental method to locally probe the 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. In lamellar-forming poly(butyl methacrylate- b-methyl methacrylate) diblock copolymers, a strong gradient in glass transition temperature, T _g, of the higher- T _g block, 42 K over 4 nm, was mapped with nanometer resolution. These measurements also revealed a strongly asymmetric influence of the domain interface on T _g, with a much smaller dynamic gradient being observed for the lower- T _g block.

Abstract

By attaching fluorescent labels at specific locations along a diblock copolymer chain, we measure the motional heterogeneity within the self-assembled lamellar structure at nanometer-scale resolution.