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Updated: Jul 22, 2026
09:32
Cooling Rate Dependent Ellipsometry Measurements to Determine the Dynamics of Thin Glassy Films
Published on: January 27, 2016
Free-volume dynamics in glasses and supercooled liquids
John T Bendler1, John J Fontanella, M F Shlesinger
1Physics Department, US Naval Academy, Annapolis, Maryland 21402, USA.
Summary
A new defect diffusion model explains glass and liquid behaviors using positronium annihilation lifetime spectroscopy (PALS) and dielectric relaxation data. The model reveals distinct defect dynamics above and below the glass transition temperature.
Area of Science:
- Materials Science
- Physical Chemistry
- Condensed Matter Physics
Background:
- Understanding the complex behavior of glasses and glass-forming liquids is crucial for materials science.
- Existing models often struggle to reconcile various experimental observations across different temperature states.
Purpose of the Study:
- To develop and validate a free-volume theory based on the defect diffusion model (DDM).
- To interpret experimental data for poly(propylene glycol) (PPG 4000) and glycerol using the DDM.
- To elucidate the role of mobile and immobile defects in the behavior of glasses and liquids.
Main Methods:
- Developed a free-volume theory grounded in the defect diffusion model (DDM).
- Utilized positronium annihilation lifetime spectroscopy (PALS) to measure free-volume and intensity.
- Collected dielectric relaxation and electrical conductivity data.
- Applied the DDM to analyze experimental data for PPG 4000 and glycerol.
Main Results:
- The DDM successfully interprets PALS and electrical data for PPG 4000 and glycerol.
- PPG 4000 data align with a three-halves power law, while glycerol data favor a standard Vogel-Fulcher-Tammann law.
- Observed transitions in electrical conductivity and PALS free volume around 1.4-1.5 times the glass transition temperature (Tg).
- Identified dominance of mobile single defects above (1.4-1.5)Tg and immobile clustered defects below Tg.
Conclusions:
- The DDM provides a coherent framework for understanding glasses and glass-forming liquids.
- The theory successfully explains the temperature-dependent behavior of free volume and electrical properties.
- Defect dynamics significantly influence the macroscopic properties of these materials.
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