Glass transition behavior can be probed by dipolar interactions
Glass transition behavior can be probed by dipolar interactions lead image
Glass-forming molecular liquids undergo a peculiar transition under decreasing temperature. The mobility of individual molecules in the liquid — known as its structural relaxation — slows down, and their relative positions — which change as the fluid flows — eventually become static. The result is a solid glass with a disordered structure at the atomic and molecular level.
This phenomenon, known as the glass transition, remains a puzzle, with ongoing debate on the role of dipolar intermolecular interactions.
Silvia Arrese-Igor sought to resolve this question by contrasting entropy fluctuation measurements, which comprehensively assess all the relevant configurational degrees of freedom, with dipolar relaxation. She found a one-to-one relationship between the primary structural relaxation dynamics observed by both probes, indicating a critical role for dipolar intermolecular interactions.
Arrese-Igor studied glass-forming liquid samples just before the glass transition. She compared spectroscopy experiments, which characterize the dipole dynamics and structural relaxation of the glass, to entropy fluctuation measurements, which indicate the system’s structural and motional degrees of freedom.
“Systematic comparison has allowed establishing a solid relationship that holds even when dipolar cross-correlations dominate the dielectric signal,” said Arrese-Igor. “The time distribution of the structural relaxation changes with the dielectric strength, so this result challenges the idea of a universal spectral shape for the structural relaxation.”
Understanding structural relaxation can have significant impacts on applications that require careful control of molecular mobility and transport, such as surfactants and ionic liquids.
“The range of materials capable of forming a glass is very diverse in terms of their structural, chemical, and physical properties, complicating generalization and full understanding of the glass transition phenomena,” Arrese-Igor said.
Source: “Correlation between entropy fluctuations and the dielectric relaxation of glass forming systems: the central role of dipolar-dipolar cross correlations,” by Silvia Arrese-Igor, Journal of Chemical Physics (2025). The article can be accessed at https://doi.org/10.1063/5.0250874 .
