Dynamics of Glass-Forming Liquids

Glass-forming liquids exhibit a dramatic slowing of molecular motion as they are cooled or compressed, yet undergo only subtle changes in average structure. In the supercooled regime, relaxation follows a two-step pattern: a fast β process associated with local cage rattling and a much slower α process linked to collective structural rearrangements. The emergence of dynamic heterogeneity—regions of differing mobility—signals growing correlations in space and time. Two principal frameworks seek to explain these phenomena. Dynamic facilitation theory attributes slowing to sparse, activated excitations that propagate relaxation events, while thermodynamic scenarios invoke an underlying entropy crisis and cooperatively rearranging regions (CRRs) whose size grows as configurational entropy diminishes. Mode Coupling Theory provides a predictive onset for non‐Arrhenius behaviour but must be supplemented by activated processes at lower temperatures. Advances in particle‐resolved experiments, high‐performance simulations and machine learning have begun to unravel the microscopic origin of relaxation, revealing fractal geometries of CRRs and local structural motifs that forecast slow dynamics. Understanding these mechanisms is essential for tailoring advanced glasses and amorphous materials in applications ranging from pharmaceuticals to optical fibres.

Research from Nature Portfolio

Recent studies have combined state‐of‐the‐art GPU simulations with colloidal experiments to pinpoint the elementary relaxation events in deeply supercooled liquids. These works demonstrate that excitations follow a Boltzmann distribution and remain microscopic in timescale, while CRRs exhibit fractal dimensions that increase as configurational entropy falls. A clear separation emerges between fast, local excitations and slower, cooperative rearrangements, shedding light on the buildup of dynamic heterogeneity below the Mode Coupling crossover.

Another line of inquiry employs unsupervised machine learning to derive purely structural order parameters that correlate strongly with regions of slow dynamics. By analysing single‐snapshot configurations, these approaches autonomously identify local motifs whose spatial distribution predicts both β and α relaxation patterns without prior dynamical input.

Studies of two‐dimensional glass formers using advanced Monte Carlo schemes have accessed equilibrium states at unprecedentedly low temperatures, revealing that a true thermodynamic glass transition can occur at zero temperature. This transition is marked by a diverging static correlation length and an entropy crisis, demonstrating that finite‐dimensional glass formers can undergo a well‐defined thermodynamic transition.

Dynamics of Glass-Forming Liquids publication trend

The graph below shows the total number of articles in dynamics of glass-forming liquids across all publications each year (not limited to Nature Index journals).

Technical terms

Supercooled liquid: A liquid cooled below its freezing point without crystallising, exhibiting greatly slowed dynamics.

Glass transition: The gradual transformation of a supercooled liquid into an amorphous solid marked by dramatic growth of relaxation times.

Dynamic heterogeneity: Spatial variation in mobility within a supercooled liquid, giving rise to fast and slow regions.

Cooperatively rearranging region (CRR): A cluster of particles that undergo collective rearrangement to facilitate structural relaxation.

Dynamic facilitation: A theoretical view in which rare, local excitations trigger neighbouring relaxation events, propagating mobility.

Configurational entropy: The entropy associated with the number of distinct amorphous arrangements accessible at a given temperature.

Correlation length: A measure of the spatial extent over which particle motions or structural fluctuations are correlated.

References

1. Probing excitations and cooperatively rearranging regions in deeply supercooled liquids. Nature Communications (2023).
2. Scaling Description of Dynamical Heterogeneity and Avalanches of Relaxation in Glass-Forming Liquids. Physical Review X (2023).
3. Surface premelting and melting of colloidal glasses. Science Advances (2023).
4. Excitations Are Localized and Relaxation Is Hierarchical in Glass-Forming Liquids. Physical Review X (2011).
5. Revealing Hidden Structural Order Controlling Both Fast and Slow Glassy Dynamics in Supercooled Liquids. Physical Review X (2018).
6. Mode-Coupling Theory of the Glass Transition: A Primer. Frontiers in Physics (2018).
7. Zero-temperature glass transition in two dimensions. Nature Communications (2019).