Thermal stabilities of a molecularly stepped PMMA substrate prepared by thermal nanoimprinting and isolated PMMA chains deposited on it evaluated by high-temperature atomic force microscopy

Polymer surfaces are believed to have high mobility, and the glass transition temperature (Tg) of these surfaces is significantly decreased compared to that of the bulk. In this study, we prepared a molecularly stepped poly(methyl methacrylate) (PMMA) substrate by thermally nanoimprinting a PMMA plate with an atomically stepped sapphire substrate and PMMA isolated chains deposited on it by the Langmuir-Blodgett technique. The imprinted PMMA surface with a step height of ~0.2 nm and isolated PMMA chains deposited on it could be observed at the molecular level up to the PMMA bulk Tg by in situ high-temperature atomic force microscopy, indicating that the PMMA surface and the PMMA chains deposited on it have thermal stability close to the bulk PMMA Tg and that no significant decrease in Tg was observed. The significant thermal stability of the surface of the imprinted PMMA substrate and deposited PMMA chains is unexpected and differs from the results based on our present understanding of the polymer surfaces. We evaluated the thermal stability of a molecularly stepped poly(methyl methacrylate) (PMMA) substrate prepared by thermal nanoimprinting and PMMA isolated chains deposited on it by in situ high-temperature atomic force microscopy. The imprinted PMMA surface and isolated PMMA chains on it could be observed at the molecular level up to the glass transition temperature (Tg) of the bulk PMMA and no significant decrease in Tg was observed. The significant thermal stability of them is unexpected and differs from our present understanding of the polymer surfaces.