Physicists solve 20-year-old debate surrounding glassy surfaces

February 28, 2014
Waterloo physicists solve 20-year-old debate surrounding glassy surfaces
In a series of experiments, University of Waterloo researchers and colleagues started with very thin slices of polystyrene stacked to create tiny staircase-like steps about 100-nanometers 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 paper investigated how the top layer of glassy polymers is always moving despite the layers underneath being frozen or solid-like. The gold graph represents how the top surface is moving at one point in time. Credit: University of Waterloo

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

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.

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.

Their groundbreaking work was published in the prestigious scientific journal, Science, this week.

"Glasses are fascinating materials. At low temperatures they're solid, and at higher temperatures they're liquid. At intermediate temperatures, it's hard to consider them as only one or the other," said Professor Forrest. "Surfaces of glassy polymers shouldn't flow below the temperature, but they do. The question is why."

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 .

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.

Graph showing how the top surface of a glassy polymer moves like a liquid.Graph showing how the top surface of a glassy polymer moves like a liquid

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 .

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.

Being able to calculate how these nanostructures may evolve over time and under what conditions will bring engineers a step further towards making nanotechnology an everyday reality.

Explore further: Study suggests viscous materials do not follow standard laws below a sub-melting point threshold

More information: Science Vol. 343 no. 6174 pp. 994-999. DOI: 10.1126/science.1244845

Related Stories

A new way of making glass

November 9, 2012

(Phys.org)—A new way to make glass has been discovered by a collaboration of researchers at the Universities of Düsseldorf and Bristol using a method that controls how the atoms within a substance are arranged around each ...

Sneaking up on the glassy transition of water

September 26, 2011

Rapid cooling of ordinary water or compression of ordinary ice: either of these can transform normal H2O into an exotic substance that resembles glass in its transparency, brittleness, hardness, and luster. Unlike everyday ...

Cracking a controversial solid state mystery

February 6, 2009

(PhysOrg.com) -- Scientists can easily explain the structural order that makes steel and aluminium out of molten metal. And they have discovered the molecular changes that take place as water turns to ice. But, despite the ...

New experiment opens window on glasses

June 10, 2013

(Phys.org) —For the first time, scientists have mapped the structure of a metallic glass on the atomic scale, bringing them closer to understanding where the liquid ends and the solid begins in glassy materials.

Recommended for you

Theory lends transparency to how glass breaks

January 16, 2017

Over time, when a metallic glass is put under stress, its atoms will shift, slide and ultimately form bands that leave the material more prone to breaking. Rice University scientists have developed new computational methods ...

A novel way to put flame retardant in a lithium ion battery

January 16, 2017

(Phys.org)—A team of researchers at Stanford University has found a novel way to introduce flame retardant into a lithium ion battery to prevent fires from occurring. In their paper published in the journal Science Advances, ...

Self-assembling particles brighten future of LED lighting

January 16, 2017

Just when lighting aficionados were in a dark place, LEDs came to the rescue. Over the past decade, LED technologies—short for light-emitting diode—have swept the lighting industry by offering features such as durability, ...

Phase transition discovery opens the door to new electronics

January 16, 2017

A group of European scientists led by researchers at TU Delft has discovered how phase transitions propagate throughout materials called nickelates. The discovery improves our understanding of these novel materials, which ...

Electron diffraction locates hydrogen atoms

January 13, 2017

Diffraction-based analytical methods are widely used in laboratories, but they struggle to study samples that are smaller than a micrometer in size. Researchers from the Laboratoire de cristallographie et sciences des matériaux ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.