Identification of Concealed Transition Phase Between Liquid and Solid by Scientists

(Left) When above a specific onset temperature, a 2D material demonstrates regular liquid activity, where all particles are uniformly mobile (colored in yellow). (Right) Below such temperature, it turns supercooled, commencing rigidity that results in some particles being mobile (yellow) amidst solid-like ‘immobile’ zones (blue). Credit goes to Kranthi Mandadapu.

Enhancing our knowledge of glassy dynamics might assist scientists in comprehending why a liquid appears solid and in the creation of new functional materials.

The researchers have recognized a concealed transition phase in amorphous substances like plastics and glass. By merging theory, simulations, and former research, they have noticed that these materials’ molecules become highly viscous at a particular “onset temperature,” shifting from a liquid state to a solid one. This could open doors for the creation of new amorphous materials for different purposes, such as medical instruments and medication delivery.

Anything created from plastic or glass is referred to as an amorphous substance. Contrary to many materials that solidify into crystalline forms, the atoms and molecules in amorphous materials never align to create crystals when chilled. In fact, even though we often view plastic and glass as “solids,” they remain in a more precise condition of a supercooled liquid that flows at an extremely slow pace. These “glassy dynamic” materials, though prevalent in our daily lives, their transformation into rigidity on a microscopic level has remained a mystery for a long time.

Researchers at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) have now uncovered molecular actions in supercooled liquids, denoting a hidden transition phase from a liquid to a solid.

This enhanced understanding pertains to common substances like plastics and glass, and could enable scientists to produce new amorphous materials for applications such as medical equipment, drug administration, and additive production.

Unveiling Scientific Insights into Glassy Dynamics

In particular, by integrating theory, computer-based simulations, and past experimentations, the researchers clarified that when cooled, the molecules in these substances remain disordered like a liquid until a sudden shift to a solid-like state occurs at a temperature named the onset temperature, becoming so viscous that movement is nearly nonexistent. This commencement of rigidity, a phase transition previously undiscovered, distinguishes supercooled liquids from regular ones.

Credit: Kranthi Mandadapu

Kranthi Mandadapu, a staff scientist at Berkeley Lab’s Chemical Sciences Division and a professor of chemical engineering at the University of California, Berkeley, who headed the study (published in PNAS), remarked, “Our theory anticipates the onset temperature observed in model systems and elucidates why supercooled liquids act like solids around that temperature, even though their structural composition remains liquid-like.”

Any supercooled liquid fluctuates between various molecular arrangements, leading to localized particle activities known as excitations. In the proposed theory, Mandadapu, along with postdoctoral researcher Dimitrios Fraggedakis and graduate student Muhammad Hasyim, regarded these excitations in a 2D supercooled liquid akin to defects in a crystalline solid. They suggest that with the liquid’s temperature rising to the onset temperature, every instance of a bound defect pair broke into an unbound one. Precisely at this temperature, the defect unbinding causes the system to lose its rigidity and commence behaving as a regular liquid.

“The onset temperature for glassy dynamics is analogous to a melting temperature that transitions a supercooled liquid to a liquid. This should be pertinent to all supercooled liquids or glassy structures,” Mandadapu noted.

“The entire endeavor is to comprehend microscopically what distinguishes the supercooled liquid from a high-temperature liquid,” – Kranthi Mandadapu.

Advancing Research

The theory and simulations encapsulated other vital characteristics of glassy dynamics, like the short-term observation that a minority of particles moved while the majority of the liquid stayed stationary.

“The complete endeavor is to grasp microscopically what differentiates the supercooled liquid and a high-temperature liquid,” Mandadapu stated.

Mandadapu and his team predict they can expand their model to 3D systems and intend to broaden it to explain how localized movements lead to neighboring excitations, resulting in the relaxation of the entire liquid. Collectively, these elements could provide a coherent microscopic depiction of how glassy dynamics originate, aligning with cutting-edge observations.

“It’s captivating from a fundamental scientific standpoint to investigate why these supercooled liquids display incredibly distinct dynamics from the regular liquids we are familiar with,” Mandadapu commented.

Reference: “Inherent-state melting and the onset of glassy dynamics in two-dimensional supercooled liquids” by Dimitrios Fraggedakis, Muhammad R. Hasyim, and Kranthi K. Mandadapu, 31 March 2023, Proceedings of the National Academy of Sciences.
DOI: 10.1073/pnas.2209144120

The Department of Energy’s Office of Science supported this research.

Frequently Asked Questions (FAQs) about Phase Transition

More about Phase Transition

• Researchers Identify Hidden Phase Transition in Supercooled Liquids – Lawrence Berkeley National Laboratory article
• Proceedings of the National Academy of Sciences – Research paper source
• Glassy Dynamics and Material Science – Scientific insights on glassy dynamics and materials
• Understanding Amorphous Materials – ScienceDaily overview of amorphous materials
• Importance of Glassy Dynamics – Nature Reviews Materials article on the significance of glassy dynamics