1. Glass transition in thin supported polystyrene films probed by temperature-modulated ellipsometry in vacuum.
- Author
-
Efremov MY, Kiyanova AV, Last J, Soofi SS, Thode C, and Nealey PF
- Subjects
- Nitrogen chemistry, Oxidation-Reduction, Surface Properties, Vacuum, Glass chemistry, Phase Transition, Polystyrenes chemistry, Temperature
- Abstract
Glass transition in thin (1-200 nm thick) spin-cast polystyrene films on silicon surfaces is probed by ellipsometry in a controlled vacuum environment. A temperature-modulated modification of the method is used alongside a traditional linear temperature scan. A clear glass transition is detected in films with thicknesses as low as 1-2 nm. The glass transition temperature (T(g)) shows no substantial dependence on thickness for coatings greater than 20 nm. Thinner films demonstrate moderate T(g) depression achieving 18 K for thicknesses 4-7 nm. Less than 4 nm thick samples are excluded from the T(g) comparison due to significant thickness nonuniformity (surface roughness). The transition in 10-20 nm thick films demonstrates excessive broadening. For some samples, the broadened transition is clearly resolved into two separate transitions. The thickness dependence of the glass transition can be well described by a simple 2-layer model. It is also shown that T(g) depression in 5 nm thick films is not sensitive to a wide range of experimental factors including molecular weight characteristics of the polymer, specifications of solvent used for spin casting, substrate composition, and pretreatment of the substrate surface.
- Published
- 2012
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