Thin polymer films in contact with a substrate serve as the enabling material for a range of emerging technologies, including nanoimprint and block copolymer lithography for microelectronics, membranes for efficient separations and drug delivery, and semiconductors for organic solar cells and electronics. A critical step in film production is thermal annealing the polymer film in the melt state to remove excess solvent, relax residual stresses and thermal history induced during formation, and—in the case of block copolymer films—induce self-assembly. During prolonged melt-state annealing, monomer-substrate interactions on the order of kBT can lead to the formation of an irreversibly adsorbed (or physically bound) nanolayer. This adsorbed layer has been linked to changes in thin film properties and its formation has many implications in determining the glass transition temperature (Tg) of confined polymer films– which is known to depend heavily on interfacial interactions. PCCM researchers are investigating how the Tg of this adsorbed layer is influenced by the free surface and employing a fluorescence technique to directly measure the Tg of the adsorbed layer buried in a film.
