Tag Archives: Elie Raphael

Mystery of glass—shattered and Happy Canada Day!

I’m pretty sure I’ve said this before but a repetition can’t hurt, “I love glass both for the art and the mystery.” Naturally, I am of two minds about this ‘shattered’ glass mystery from the University of Waterloo (Canada).

A June 29, 2015 University of Waterloo news release (also on EurekAlert) provides a teasing (for impatient people like me) introduction before describing the solution to the mystery,

A physicist at the University of Waterloo is among a team of scientists who have described how glasses form at the molecular level and provided a possible solution to a problem that has stumped scientists for decades.

Their simple theory is expected to open up the study of glasses to non-experts and undergraduates as well as inspire breakthroughs in novel nanomaterials.

The paper published by physicists from the University of Waterloo, McMaster University, ESPCI ParisTech and Université Paris Diderot appeared in the prestigious peer-reviewed journal, Proceedings of the National Academy of Sciences (PNAS).

Glasses are much more than silicon-based materials in bottles and windows. In fact, any solid without an ordered, crystalline structure — metal, plastic, a polymer — that forms a molten liquid when heated above a certain temperature is a glass. Glasses are an essential material in technology, pharmaceuticals, housing, renewable energy and increasingly nano electronics.

“We were surprised — delighted — that the model turned out to be so simple,” said author James Forrest, a University Research Chair and professor in the Faculty of Science. “We were convinced it had already been published.”

The theory relies on two basic concepts: molecular crowding and string-like co-operative movement. [emphasis mine] Molecular crowding describes how molecules within glasses move like people in a crowded room. As the number of people increase, the amount of free volume decreases and the slower people can move through the crowd. Those people next to the door are able to move more freely, just as the surfaces of glasses never actually stop flowing, even at lower temperatures.

The more crowded the room, the more you rely on the co-operative movement with your neighbours to get where you’re going. Likewise, individual molecules within a glass aren’t able to move totally freely. They move with, yet are confined by, strings of weak molecular bonds with their neighbours.

Theories of crowding and cooperative movement are decades old. This is the first time scientists combined both theories to describe how a liquid turns into a glass.

“Research on glasses is normally reserved for specialists in condensed matter physics,” said Forrest, who is also an associate faculty member at Perimeter Institute for Theoretical Physics and a member of the Waterloo Institute for Nanotechnology.  “Now a whole new generation of scientists can study and apply glasses just using first-year calculus.”

Their theory successfully predicts everything from bulk behaviour to surface flow to the once-elusive phenomenon of the glass transition itself. Forrest and colleagues worked for 20 years to bring theory in agreement with decades of observation on glassy materials.

An accurate theory becomes particularly important when trying to understand glass dynamics at the nanoscale. This finding has implications for developing and manufacturing new nanomaterials, such as glasses with conductive properties, or even calculating the uptake of glassy forms of pharmaceuticals.

Here’s a link to and a citation for the paper,

Cooperative strings and glassy interfaces by Thomas Salez, Justin Salez, Kari Dalnoki-Veress, Elie Raphaël, and James A. Forrest. PNAS (Proceedings of the National Academy of Sciences) Published online before print June 22, 2015, doi: 10.1073/pnas.1503133112

This paper is behind a paywall.

Finally and again, Happy Canada Day!

Glass is a challenge to measure but scientists at Canada’s University of Waterloo have figured out how

Glass, as many folks know, has a dual nature, being simultaneously both liquid and solid, making truly accurate measurement a bit of a challenge.  A March 3, 2014 news item on Azonano notes that scientists at Canada’s Waterloo University have solved the surface measurement problems with glass,

University of Waterloo physicists have succeeded in measuring how the surfaces of glassy materials flow like a liquid, even when they should be solid.

Understanding the mobility of glassy surfaces has implications for the design and manufacture of thin-film coatings and also sets practical limits on how small we can make nanoscale devices and circuitry.

The work is the culmination of a project carried out by a research team led by Professor James Forrest and doctoral student Yu Chai from the University of Waterloo as well as researchers from École Superieure de Physique et de Chimie Industrielles in France and McMaster University [Canada].

A Feb. 28  2014 University of Waterloo news release (also on EurekAlert) by Katharine Tuerke, which originated the news item, describes the research in further detail,

“Common sense would tell you that if a material is solid, it’s solid everywhere. But we’ve shown that a solid isn’t a solid everywhere,” says James Forrest, a professor in Waterloo’s Department of Physics and Astronomy.  “It’s almost solid everywhere –  except a few nanometers at the surface.”

A series of simple and elegant experiments were the solution to a problem that has been plaguing condensed matter physicists for the past 20 years. The experiments revealed that at a certain temperature range, solid glassy materials actually have a very thin liquid-like layer at the surface.

Glass is much more than the material in bottles and windows. In fact, any solid without an ordered, crystalline structure is considered a glassy material, so metals, small molecules, and polymers can all be made into glassy materials.

Polymers, the building block of all plastics, are almost always glassy rather than crystalline. These materials undergo a transition between a brittle solid and a molten liquid in a narrow temperature range, which encompasses the so-called glass transition temperature.

In a series of experiments, Forrest and colleagues started with very thin slices of polystyrene stacked to create tiny staircase-like steps about 100-nanometres high – less than 0.001 per cent the thickness of a human hair. They then measured these steps as they became shorter, wider and less defined over time.

The simple 2-dimensional profile of this surface step allowed the physicists to numerically model the changes to the surface’s geometry above and below the glass transition temperature.

Results show that above the transition temperature, polystyrene flows entirely like a liquid; but below this temperature the polymer becomes a solid with a thin liquid-like layer at the surface.

Forrest is also a University Research Chair, a member of the Waterloo Institute for Nanotechnology and an associate faculty member at the Perimeter Institute.

The project team also includes Kari Dalnoki-Veress and J.D. McGraw from McMaster University and Thomas Salez, Michael Benzaquen and Elie Raphael of the École Superieure de Physique et de Chimie Industrielles in Paris.

The researchers have provided a 21 second animation to illustrate their work,

Here’s a link to and a citation for the research paper,

A Direct Quantitative Measure of Surface Mobility in a Glassy Polymer by Y. Chai, T. Salez, J. D. McGraw, M. Benzaquen, K. Dalnoki-Veress, E. Raphaël, & J. A. Forrest. Science 28 February 2014: Vol. 343 no. 6174 pp. 994-999 DOI: 10.1126/science.1244845

This paper is behind a paywall.