Probing cooperative liquid dynamics with the mean square displacement.

Area of Science:

• Materials Science
• Condensed Matter Physics
• Physical Chemistry

Background:

• Fragility in glass formers is a key property related to their viscosity and relaxation dynamics.
• Anharmonicity and cooperative rearrangement are proposed mechanisms influencing glass fragility.

Purpose of the Study:

• To elucidate the contributions of anharmonicity and the Adam-Gibbs mechanism to glass fragility.
• To establish a method for separately measuring these two influential factors.

Main Methods:

• Analysis of literature data on picosecond mean square displacements.
• Simultaneous measurement of liquid and crystal phases in the coexistence region.

Main Results:

• Anharmonicity accounts for approximately 50% of glass fragility, varying among different glass formers.
• The remaining fragility is explained by the Adam-Gibbs mechanism, involving growing cooperatively rearranging regions.

Conclusions:

• Both anharmonicity and cooperative rearrangement significantly contribute to glass fragility.
• Simultaneous measurements in the coexistence region enable the distinct quantification of these two mechanisms.