Effect of Spatial Confinement on the Glass-Transition Temperature of Patterned Polymer Nanostructures

• Published in: Nano letters Vol. 7; no. 3; pp. 713 - 718
• Main Authors: Mundra, Manish K, Donthu, Suresh K, Dravid, Vinayak P, Torkelson, John M
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01.03.2007
• Subjects: Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Equations of state, phase equilibria, and phase transitions; Exact sciences and technology; Glass transitions; Materials science; Nanoscale materials and structures: fabrication and characterization; Other topics in nanoscale materials and structures; Physics; Specific phase transitions; Ultrathin films; Temperature dependence; TGS; Confinement; Transition temperature; Electron beam lithography; Thermogravimetry; Fluorescence; Nanostructures; Silica; Glass transition temperature; Thin films; Glass transition; PMMA; Surface area; Polymers
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/nl062894c

Poly(methyl methacrylate) (PMMA) nanostructures embedded with a fluorescence tag are fabricated using electron beam lithography on oxidized silicon substrates. The glass transition temperatures (T gs) of these one-dimensional (1-D) nanostructures (parallel lines) are measured by monitoring their temperature-dependent fluorescence intensities, revealing substantial differences between the T gs of the nanostructures and the thin films from which they were fabricated. For example, the T g of 50-nm-wide PMMA nanolines on silica is ∼15 K lower than that of a PMMA film on silica of the same 18 nm thickness. Attractive PMMA−silica interfacial interactions increase the T g, while free surfaces decrease the T g of PMMA in ultrathin films relative to bulk PMMA. Thus, the significant differences between the T gs 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.