Selectively Probing the Glass Transition Temperature in Multilayer Polymer Films: Equivalence of Block Copolymers and Multilayer Films of Different Homopolymers

Abstract

The temperature dependence of the fluorescence of trace levels of pyrene was employed to measure the glass transition temperatures (Tgs) of polystyrene (PS) domains within ultrathin films of poly(styrene-block-methyl methacrylate) (P(S-b-MMA)) and poly(styrene-block-2-vinylpyridine) (P(S-b-2VP)) diblock copolymers supported on silica after self-assembly into lamellar morphologies. The PS domains within the two block copolymers exhibited dramatically different Tg−nanoconfinement behavior. The Tgs of the PS domains within the P(S-b-MMA) films were observed to decrease with decreasing film thickness in accordance with Tg reductions observed for single-layer PS homopolymer films; in contrast, the Tg of the PS domains within the P(S-b-2VP) films exhibited no change within experimental uncertainty upon confinement. The Tgs of the block copolymer films showed excellent agreement with those of multilayer films constructed from homopolymer layers with an equivalent morphology, indicating that chain connectivity ac...