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Cooling Rate Dependent Ellipsometry Measurements to Determine the Dynamics of Thin Glassy Films

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Measuring the surface dynamics of glassy polymers.

Z Fakhraai¹, J A Forrest

¹Department of Physics and Astronomy and Guelph-Waterloo Physics Institute, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada.

Science (New York, N.Y.)

|February 2, 2008

Summary

Polymer surfaces exhibit enhanced mobility below the glass transition temperature, unlike the bulk material. This surface motion is less dependent on temperature, even at very low temperatures.

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Area of Science:

Polymer Science
Materials Science
Surface Science

Background:

Polymer chain segments slow down below the glass transition temperature (Tg).
Debate exists on whether surface and thin-film polymer dynamics differ from bulk behavior.
Understanding surface dynamics is crucial for polymer applications.

Purpose of the Study:

To investigate polymer surface dynamics below the bulk glass transition temperature.
To directly probe and quantify surface mobility in polystyrene.
To compare surface relaxation behavior with bulk alpha relaxation.

Main Methods:

Created nanodeformations on polystyrene surfaces using gold nanospheres.
Measured time-dependent relaxation of these surface deformations.
Analyzed relaxation as a function of temperature (277–369 K).

Main Results:

Observed surface relaxation at all tested temperatures, indicating enhanced surface mobility.
Surface dynamics deviated more from bulk behavior as temperature decreased below Tg.
Surface relaxation time showed weaker temperature dependence than bulk alpha relaxation.

Conclusions:

Provided direct evidence for enhanced polymer surface mobility relative to the bulk.
Surface dynamics are less sensitive to temperature changes below Tg compared to bulk.
The study offers insights into the unique behavior of polymers at surfaces.

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