Related Experiment Video
Updated: Aug 14, 2026
11:03
An Analog Macroscopic Technique for Studying Molecular Hydrodynamic Processes in Dense Gases and Liquids
Published on: December 4, 2017
Crossover of quasi-localized dynamics and diffusion in supercooled liquids
Federico Caporaletti1,2, Simone Capaccioli3, Dimitrios Bessas4
1Laboratory of Polymer and Soft Matter Dynamics, Experimental Soft Matter and Thermal Physics, Université libre de Bruxelles, Brussels, Belgium.
Nature Physics
|August 13, 2026
Summary
Secondary relaxation (βJG relaxation) in glasses is not independent of α relaxation. This study reveals βJG relaxation as critical molecular rattling within cages before diffusion, impacting glass properties.
Area of Science:
- Materials Science
- Condensed Matter Physics
- Chemical Physics
Background:
- Secondary relaxation (βJG relaxation) is a key dynamical process in supercooled liquids and glasses, distinct from α relaxation.
- It influences crucial properties like crystallization propensity and mechanical response.
- Previous studies often linked βJG relaxation to quasi-localized particle motion, typically investigated through dielectric and mechanical spectroscopy.
Purpose of the Study:
- To investigate the nature of βJG relaxation in a hydrogen-bonded glass former using a novel X-ray technique.
- To determine the relationship between α and βJG relaxation processes.
- To elucidate the microscopic dynamics associated with βJG relaxation.
Main Methods:
- Utilized a wavevector-resolved X-ray technique.
- Accessed microscopic, real-space information on molecular dynamics.
- Analyzed the mean-squared molecular displacement preceding diffusion.
Main Results:
- Demonstrated that α and βJG relaxations are not independent processes.
- Provided evidence linking βJG relaxation to sublinear growth in mean-squared molecular displacement.
- Showed that βJG relaxation precedes the onset of diffusion.
Conclusions:
- βJG relaxation is intrinsically linked to the α relaxation process.
- βJG relaxation represents the critical rattling of molecules within their cages before escaping.
- This finding clarifies the fundamental dynamics governing glass behavior.
Related Concept Videos
02:39Phase Transitions: Vaporization and Condensation
The physical form of a substance changes on changing its temperature. For example, raising the temperature of a liquid causes the liquid to vaporize (convert into vapor). The process is called vaporization—a surface phenomenon. Vaporization occurs when the thermal motion of the molecules overcome the intermolecular forces, and the molecules (at the surface) escape into the gaseous state. When a liquid vaporizes in a closed container, gas molecules cannot escape. As these gas phase molecules...
02:39Phase Transitions: Melting and Freezing
Heating a crystalline solid increases the average energy of its atoms, molecules, or ions, and the solid gets hotter. At some point, the added energy becomes large enough to partially overcome the forces holding the molecules or ions of the solid in their fixed positions, and the solid begins the process of transitioning to the liquid state or melting. At this point, the temperature of the solid stops rising, despite the continual input of heat, and it remains constant until all of the solid is...
01:27Two Components: Liquid–Liquid Systems
A pressure-composition phase diagram explicitly describes the behavior of an ideal solution of two volatile liquids under varying pressures and compositions. A pressure-composition diagram has two main curves. The bubble point curve represents the plot of pressure versus liquid mole fraction. It indicates the pressure at which the first bubble of vapor forms from the liquid phase as the system pressure decreases.The dew point curve is the pressure versus vapor mole fraction. It indicates the...
01:09Theories of Dissolution: The Danckwerts' Model and Interfacial Barrier Model
Various dissolution theories provide insight into the factors that influence the dissolution rate. Danckwerts' Model suggests that turbulence, rather than a stagnant layer, characterizes the dissolution medium at the solid-liquid interface. In this model, the agitated solvent contains macroscopic packets that move to the interface via eddy currents, facilitating the absorption and delivery of the drug to the bulk solution. The regular replenishment of solvent packets maintains the concentration...
01:15Theories of Dissolution: Diffusion Layer Model
Dissolution, the process by which drug particles dissolve in a solvent, is explained by the diffusion layer model, a theoretical framework that simulates the absorption of oral drugs and allows us to analyze experimental data.
This process starts with a thin layer, saturated with the drug, forming at the interface between the solid and liquid. The solute then diffuses from this layer into the main solution. The Noyes-Whitney equation suggests that the rate of dissolution relies on the diffusion...
This process starts with a thin layer, saturated with the drug, forming at the interface between the solid and liquid. The solute then diffuses from this layer into the main solution. The Noyes-Whitney equation suggests that the rate of dissolution relies on the diffusion...
01:29Nonideal Two-Component Liquid Solutions
Nonideal liquid solutions, also known as real solutions, do not strictly follow Raoult's law. Raoult's law is a rule of thumb in physical chemistry. However, not all mixtures adhere to this law due to varying molecular interactions. For example, in an acetone/chloroform solution, the individual vapor pressures of the components are lower than expected, resulting in a total vapor pressure below that predicted by Raoult's law, causing a negative deviation.On the other hand, in an ethanol/water...