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Evolution of excess wing and beta-process in simple glass formers
Catalin Gainaru1, Robert Kahlau, Ernst A Rössler
1Physikalisches Institut, Universität Bayreuth, Bayreuth 95440, Germany. catalin.gainaru@uni-dortmund.de
The Journal of Chemical Physics
|November 18, 2009
Summary
Dielectric loss spectra reveal that even when not obvious, secondary relaxations in glass formers are present. An excess wing and beta-relaxation contribute to the alpha-relaxation peak, even in supercooled liquids.
Area of Science:
- Materials Science
- Condensed Matter Physics
- Physical Chemistry
Background:
- Dielectric loss spectra analysis is crucial for understanding the dynamics of glass-forming liquids.
- Secondary relaxations, including beta-relaxation and excess wing contributions, complicate the interpretation of alpha-relaxation peaks in these systems.
- Previous studies often struggled to resolve these overlapping relaxation processes, particularly when secondary peaks were not clearly discernible.
Purpose of the Study:
- To analyze dielectric loss spectra of glass-forming liquids, focusing on systems where secondary relaxation peaks are not immediately apparent.
- To investigate the nature and contributions of the 'excess wing' and beta-relaxation to the overall alpha-relaxation peak shape.
- To determine if excess wing and beta-relaxation are fundamental components of glass-forming liquid dynamics.
Main Methods:
- Analysis of dielectric loss spectra from various glass-forming liquid systems.
- Focus on systems where the high-frequency flank of the alpha-relaxation appears dominated by an 'excess wing'.
- Conducting aging experiments to probe the dynamic processes contributing to the relaxation spectra.
Main Results:
- The alpha-relaxation peak shape in supercooled liquids requires characterization by two parameters, even when secondary relaxations are not obvious.
- Aging experiments demonstrate that the high-frequency flank of the alpha-relaxation is superimposed by contributions from an excess wing and a beta-relaxation peak.
- The excess wing is identified as an independent dynamic feature, distinct from both alpha- and beta-relaxation.
Conclusions:
- Both excess wing and beta-relaxation are always present in glass-forming liquids, although their relative strengths vary significantly between different materials.
- The 'excess wing' is not an artifact of alpha- or beta-relaxation but a distinct relaxation process that evolves independently.
- A comprehensive understanding of glass-forming liquid dynamics necessitates accounting for these superimposed relaxation processes.
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