Glass Transitions

The glass transition temperature is an important materials property. It is the temperature at which many materials soften upon heating and lose their ability to hold their shape. For more than 15 years, the reason why the glass transition temperature of some polymers confined in nanometer films decreases with decreasing film thickness has remained elusive. A study by Professor Ophelia Tsui, postdocs Zhaohui Yang and Yoshihisa Fujii and collaborators shows that the cause is attributable to a thin, high-mobility surface layer present at the free surface of the films. Their result demonstrates that the surface layer lowers the glass transition temperature by providing a high-mobility flow channel to the films whereby material flow can be sustained, postponing the glass transition. This result was published in Science in June 2010.

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