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Rheological behavior of molecular vs network chalcogenide supercooled liquids
1Department of Materials Science and Engineering, University of California at Davis, Davis, California 95616, USA.
The Journal of Chemical Physics
|October 9, 2020
Summary
Supercooled glass-forming liquids exhibit unique viscoelastic properties. Molecular liquids show anomalous behavior linked to broad relaxation spectra and molecular clusters, unlike network liquids.
Area of Science:
- Materials Science
- Physical Chemistry
- Rheology
Background:
- Supercooled glass-forming liquids exhibit complex viscoelastic behavior.
- The As4S3-GeS2 binary system transitions from molecular to network structures.
- Understanding rheological differences is key to material properties.
Purpose of the Study:
- Investigate the viscoelasticity of As4S3-GeS2 liquids.
- Correlate structural changes (molecular to network) with rheological properties.
- Analyze deviations from Maxwell scaling and their origins.
Main Methods:
- Small-amplitude oscillatory shear rheometry.
- Parallel plate configuration.
- Analysis of storage modulus (G'), loss modulus (G"), and phase angle (δ).
Main Results:
- Storage modulus (G') shows anomalous scaling (n < 2) with increasing molecular content.
- Departure from Maxwell scaling observed for G'' above the crossover frequency.
- Molecular liquids display non-viscous response even at low frequencies.
- Broad relaxation spectra and molecular clusters contribute to anomalous behavior.
Conclusions:
- Anomalous viscoelasticity in molecular liquids is linked to broad relaxation spectra and molecular clusters.
- High-frequency plateau in relaxation spectra relates to molecular rotational dynamics.
- Structural differences explain the higher fragility of molecular versus network liquids.
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