What stops flows in glassy materials?

January 17, 2021

Various glass materials have been essential to the development of modern civilization due to their advantageous properties. Specifically, glasses have a liquid-like disordered structure but solid-like mechanical properties. This leads to one of the central mysteries of glasses: "Why don't glasses flow like liquids?" This question is so important that it was selected by the journal Science in 2005 as one of 125 key, unanswered scientific questions, and one of 11 unsolved important physical issues.

We can hardly observe the movements of atoms at a ~0.1 nanometer length scale and a ~1 nanosecond time scale. Fortunately, however, scientists have found that colloidal systems have similar phase behaviors as atomic systems. Colloids are regarded as big "atoms" that reveal microscopic information about phase transitions that can't be easily obtained from atomic materials.

In the past decade, colloidal glasses have drawn a lot of interest, resulting in numerous important discoveries. However, most of these studies are about spherical particles that tend to form local or intermediate-range crystalline structures. Unfortunately, such studies are not broadly applicable since most glasses are not composed of spheres and have no crystalline structure.

To counter this problem, researchers from the Institute of Mechanics of the Chinese Academy of Sciences and Hong Kong University of Science and Technology recently conducted experimental studies for the first time on glassy systems composed of nonspherical particles.

The researchers found that the monolayers of monodisperse ellipsoids are good glass formers and do not form local crystalline structures. Thus, they provide an ideal and general system for detecting the structural origin of slowing dynamics as the glass transition is approached.

In fact, glass formers have strong dynamic heterogeneities, i.e., some regions move fast and some move slow. These results show that structures with low structural entropy correspond well with slow dynamics, whereas fast relaxing (flowing) regions have high structural entropy.

In glasses composed of spherical particles, some polyhedral structures were usually regarded as responsible for the slow dynamics. However, a type of polyhedron only exists in certain systems of spheres. Structural entropy measures the level of disorder in a structure, including various specific local structures, e.g. virous polyhedra that exist in systems composed of spheres. So, the low structural entropy is a general structural feature of slow dynamics in glassy matter, which holds in systems composed of spheres and non-spheres.

In addition, the researchers observed Ising-like critical behaviors at an ideal glass transition point in both static structures and slow dynamics. Such behaviors are a quantitative feature of thermodynamic transition that explains whether glass transition is purely dynamic or thermodynamic (structural), since there are no ordering structures in glasses.

"The observation of critical behaviors in ellipsoid glasses provides much more solid quantitative evidence of the thermodynamic nature of glass transition," said WANG Yuren, corresponding author of the study. "The results shed new light on both the mysteries of glass theory and designing materials with high stability and glass forming ability."

Chinese Academy of Sciences Headquarters

Related Science Articles from Brightsurf:

75 science societies urge the education department to base Title IX sexual harassment regulations on evidence and science
The American Educational Research Association (AERA) and the American Association for the Advancement of Science (AAAS) today led 75 scientific societies in submitting comments on the US Department of Education's proposed changes to Title IX regulations.

Science/Science Careers' survey ranks top biotech, biopharma, and pharma employers
The Science and Science Careers' 2018 annual Top Employers Survey polled employees in the biotechnology, biopharmaceutical, pharmaceutical, and related industries to determine the 20 best employers in these industries as well as their driving characteristics.

Science in the palm of your hand: How citizen science transforms passive learners
Citizen science projects can engage even children who previously were not interested in science.

Applied science may yield more translational research publications than basic science
While translational research can happen at any stage of the research process, a recent investigation of behavioral and social science research awards granted by the NIH between 2008 and 2014 revealed that applied science yielded a higher volume of translational research publications than basic science, according to a study published May 9, 2018 in the open-access journal PLOS ONE by Xueying Han from the Science and Technology Policy Institute, USA, and colleagues.

Prominent academics, including Salk's Thomas Albright, call for more science in forensic science
Six scientists who recently served on the National Commission on Forensic Science are calling on the scientific community at large to advocate for increased research and financial support of forensic science as well as the introduction of empirical testing requirements to ensure the validity of outcomes.

World Science Forum 2017 Jordan issues Science for Peace Declaration
On behalf of the coordinating organizations responsible for delivering the World Science Forum Jordan, the concluding Science for Peace Declaration issued at the Dead Sea represents a global call for action to science and society to build a future that promises greater equality, security and opportunity for all, and in which science plays an increasingly prominent role as an enabler of fair and sustainable development.

PETA science group promotes animal-free science at society of toxicology conference
The PETA International Science Consortium Ltd. is presenting two posters on animal-free methods for testing inhalation toxicity at the 56th annual Society of Toxicology (SOT) meeting March 12 to 16, 2017, in Baltimore, Maryland.

Citizen Science in the Digital Age: Rhetoric, Science and Public Engagement
James Wynn's timely investigation highlights scientific studies grounded in publicly gathered data and probes the rhetoric these studies employ.

Science/Science Careers' survey ranks top biotech, pharma, and biopharma employers
The Science and Science Careers' 2016 annual Top Employers Survey polled employees in the biotechnology, biopharmaceutical, pharmaceutical, and related industries to determine the 20 best employers in these industries as well as their driving characteristics.

Three natural science professors win TJ Park Science Fellowship
Professor Jung-Min Kee (Department of Chemistry, UNIST), Professor Kyudong Choi (Department of Mathematical Sciences, UNIST), and Professor Kwanpyo Kim (Department of Physics, UNIST) are the recipients of the Cheong-Am (TJ Park) Science Fellowship of the year 2016.

Read More: Science News and Science Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.