Confinement effects on glass transition temperature, transition breadth, and expansivity: Comparison of ellipsometry and fluorescence measurements on polystyrene films

S. Kim*, S. A. Hewlett, C. B. Roth, John M Torkelson

*Corresponding author for this work

Research output: Contribution to journalArticle

104 Scopus citations

Abstract

Using ellipsometry, we characterized the nanoconfinement effect on the glass transition temperature (T gof supported polystyrene (PS) films employing two methods: the intersection of fits to the temperature (Tdependences of rubbery- and glassy-state thicknesses, and the transition mid-point between rubbery- and glassy-state expansivities. The results demonstrate a strong effect of thickness: Tg(bulk)-T(23nm)= 10̂C. The T -range needed for accurate measurement increases significantly with decreasing thickness, an effect that arises from the broadening of the transition with confinement and a region below T g where expansivity slowly decreases with decreasing T . As determined from expansivities, the T g breadth triples in going from bulk films to a 21-nm-thick film; this broadening of the transition may be a more dramatic effect of confinement than the T g reduction itself. In contrast, there is little effect of confinement on the rubbery- and glassy-state expansivities. Compared with ellipsometry, T g 's from fluorescence agree well in bulk films but yield lower values in nanoconfined films: T g(bulk) - T g(23 nm) = 15 ° C via fluorescence. This small difference in the T g confinement effect reflects differences in how fluorescence and ellipsometry report "average T g " with confinement. With decreasing nanoscale thickness, fluorescence may slightly overweight the contribution of the free-surface layer while ellipsometry may evenly weight or underweight its contribution.

Original languageEnglish (US)
Pages (from-to)83-92
Number of pages10
JournalEuropean Physical Journal E
Volume30
Issue number1
DOIs
StatePublished - Sep 1 2009

ASJC Scopus subject areas

  • Biotechnology
  • Biophysics
  • Chemistry(all)
  • Materials Science(all)
  • Surfaces and Interfaces

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