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Self-diffusion of supercooled tris-naphthylbenzene
Stephen F Swallen1, Katherine Traynor, Robert J McMahon
1Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53705, USA.
The Journal of Physical Chemistry. B
|March 6, 2009
Summary
Self-diffusion coefficients for supercooled tris-naphthylbenzene (TNB) were measured. Diffusion is significantly enhanced, deviating from predictions and revealing crossover to non-Fickian behavior in deeply supercooled TNB.
Area of Science:
- Materials Science
- Physical Chemistry
- Condensed Matter Physics
Background:
- Deeply supercooled liquids exhibit complex dynamics.
- Understanding molecular mobility is crucial for material properties.
- Tris-naphthylbenzene (TNB) is a model system for studying supercooled dynamics.
Purpose of the Study:
- To measure self-diffusion coefficients in deeply supercooled TNB.
- To investigate the transition from Fickian to non-Fickian diffusion.
- To compare diffusion data with other dynamic measurements in TNB.
Main Methods:
- Secondary ion mass spectrometry (SIMS) for concentration profile analysis.
- Preparation of isotopically labeled multilayer TNB films via vapor deposition.
- Analysis of Fickian diffusion evolution on various length and time scales.
Main Results:
- Self-diffusion coefficients were measured for deeply supercooled TNB.
- Diffusion was found to be enhanced ~100-fold at 338 K compared to Stokes-Einstein predictions.
- Fickian diffusion was observed for samples near the glass transition temperature (T(g)).
- Identified an error in previous TNB diffusion studies due to sample preparation.
Conclusions:
- The study quantifies the length scale for dynamics crossover in supercooled TNB.
- Enhanced diffusion highlights deviations from simple models in supercooled states.
- Accurate sample preparation is critical for studying Fickian diffusion in glasses.
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