title: Effect of spatial confinement on the glass-transition temperature of patterned polymer nanostructures.
abstract: Poly(methyl methacrylate) (PMMA) nanostructures embedded with a fluorescence tag are fabricated using electron beam lithography on oxidized silicon substrates. The glass transition temperatures (Tgs) of these one-dimensional (1-D) nanostructures (parallel lines) are measured by monitoring their temperature-dependent fluorescence intensities, revealing substantial differences between the Tgs of the nanostructures and the thin films from which they were fabricated. For example, the Tg of 50-nm-wide PMMA nanolines on silica is approximately 15 K lower than that of a PMMA film on silica of the same 18 nm thickness. Attractive PMMA-silica interfacial interactions increase the Tg, while free surfaces decrease the Tg of PMMA in ultrathin films relative to bulk PMMA. Thus, the significant differences between the Tgs of the 1-D and two-dimensional (2-D) forms of PMMA on silica are the result of a substantial increase in the ratio of free-surface area to interfacial area in the PMMA nanolines relative to ultrathin films.
authors.affiliation: Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, USA.
authors.forename: Manish K
authors.initials: MK
authors.lastname: Mundra
authors.forename: Suresh K
authors.initials: SK
authors.lastname: Donthu
authors.forename: Vinayak P
authors.initials: VP
authors.lastname: Dravid
authors.forename: John M
authors.initials: JM
authors.lastname: Torkelson