Chemistry 2011.org
Chemistry2011.org
All About Chemistry... 2011 and beyond

Related Stories

Scientists do glass a solid, with new theory on how it transitions from a liquid

How does glass transition from a liquid to its familiar solid state? How does this common material transport heat and sound? And what microscopic changes occur when a glass gains rigidity as it cools?

A team of researchers at NYU's Center for Soft Matter Research offers a theoretical explanation for these processes in Proceedings of the National Academy of Sciences.

Our understanding of glasses as they change state is relatively limited. This is because, unlike other materials such as metals, their constituent particles--which can be as small as a billionth of a meter in size--are in a disorganized, rather than orderly, arrangement. Understanding what in these disordered arrangements decides if the material is liquid or solid remains a long-lasting challenge of physics and chemistry.

The simplest examples of glasses are colloidal suspensions, which behave essentially as hard spheres. Beyond their conceptual interest, they also matter to scientists because they are the basis for an array of consumer products. For instance, colloidal dispersions comprise such everyday items as paint, milk, gelatin, glass, and porcelain. Moreover, understanding how they evolve from liquids to solids is of concern to medical researchers -- for example, the clotting of blood.

Colloids form a liquid at small density, but become solid when the density is increased beyond some threshold. At that point, crowding effects become important: particles are prisoners of the cage formed by their neighbors. Although they can still wiggle somewhat within their cage, they cannot escape far, forbidding flow. Why the assembly of cages can resist the wiggling of particles in the solid phase is a long-standing debate in the field. Explanations have been proposed in very abstract models, but a simple physical picture of what is going on was lacking.

In their theoretical work, spurred by laboratory observations of colloidal glasses, the researchers propose to use 19th-century concepts developed by Maxwell, the founder of electromagnetism, to study the stability of mechanical structures. Thus concepts widely used in architecture and engineering are now applied at a microscopic level in colloidal glasses. Based on these ideas, the authors developed a theory of the emergence of rigidity.

A curious outcome of their work is the prediction that the wiggling motion of particles in their cage is collective: particles dance in a very coordinated way. The structure of the material is predicted to be such that the dance has the largest amplitude it could possibly have without destroying the solid.

The authors show that this coordinated dance is quantitatively affected by the presence of weak spots in the materials. The description leads to various predictions on the dynamics of the particles, as well as the elastic response of the material and the ability to transport heat in molecular glasses.

The study's authors included Carolina Brito of the Universidade Federal do Rio Grande do Sul, Brazil as well as the following researchers in the Wyart group at NYU's Center for Soft Matter Research: Eric DeGiuli, a post-doctoral fellow, Edan Lerner, a post-doctoral fellow at the time of the study and now an assistant professor at the University of Amsterdam, and Matthieu Wyart, an associate professor in NYU's Department of Physics.

This work is supported by grants from the National Science Foundation (1236378; 1105387) as well as the NSF's MRSEC Program (DMR-0820341)

Story Source:

The above story is based on materials provided by New York University. Note: Materials may be edited for content and length.

Share this story with your friends!

Social Networking

Please recommend us on Facebook, Twitter and more:

Other social media tools

Global Partners
Feedback

Tell us what you think of Chemistry 2011 -- we welcome both positive and negative comments. Have any problems using the site? Questions?

About us

Chemistry2011 is an informational resource for students, educators and the self-taught in the field of chemistry. We offer resources such as course materials, chemistry department listings, activities, events, projects and more along with current news releases.

Events & Activities

Are you interested in listing an event or sharing an activity or idea? Perhaps you are coordinating an event and are in need of additional resources? Within our site you will find a variety of activities and projects your peers have previously submitted or which have been freely shared through creative commons licenses. Here are some highlights: Featured Idea 1, Featured Idea 2.

About you

Ready to get involved? The first step is to sign up by following the link: Join Here. Also don’t forget to fill out your profile including any professional designations.

Global Partners