Glassy dynamics in polyalcohols: intermolecular simplicity vs. intramolecular complexity

Area of Science:

• Physical Chemistry
• Materials Science
• Glass Science

Background:

• Supercooled liquids exhibit complex structural relaxation dynamics.
• Polyalcohols (PAs) are frequently used as model systems in glass science due to varying dielectric loss spectra.
• A generic line shape with a high-frequency power law (ω^-1/2) has been previously observed in supercooled liquid relaxation.

Purpose of the Study:

• To investigate the microscopic origin of structural relaxation in a series of polyalcohols (PAs).
• To determine if the generic relaxation line shape holds for PAs with varying chain lengths and intramolecular dynamics.
• To identify limitations in observing generic relaxation behavior in supercooled liquids.

Main Methods:

• Depolarized light scattering was employed to probe structural relaxation dynamics.
• A systematic series of polyalcohols (PAs) with diverse dielectric loss spectra were studied.
• Analysis focused on comparing light scattering spectra with the established generic line shape.

Main Results:

• Short-chained PAs, like glycerol, rotate as rigid entities, exhibiting spectra consistent with the generic shape.
• Long-chained PAs, such as sorbitol, show significant intramolecular dynamic contributions affecting structural relaxation.
• These intramolecular dynamics lead to systematic deviations from the generic relaxation line shape in long-chained PAs.

Conclusions:

• The microscopic origin of relaxation behavior varies significantly among different polyalcohols.
• Observing the generic relaxation shape requires probing dynamics that reflect intermolecular heterogeneity, not intramolecular effects.
• Intramolecular dynamics can mask or alter the manifestation of generic structural relaxation in supercooled liquids.