Tag Archives: A Direct Quantitative Measure of Surface Mobility in a Glassy Polymer

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.