Crystal-clear method for distinguishing between glass and fluids

May 28, 2013
Crystal-clear method for distinguishing between glass and fluids
The colloids that were used for the model: particles, each with a diameter of approximately 150 nanometers, suspended in water. The solid nucleus consists of the plastic polystyrene, the surrounding shell of a thermosensitive poly(N-isopropyl-acrylamide) network. By lowering the temperature, each individual particle's volume - and, by definition, its packing density - can be increased. Credit: HZB/M. Siebenbürger

Many solids are produced from melting. Depending on how quickly they cool off, invariably, internal tensile stresses begin to build up. One example are Prince Rupert's Drops, or Dutch tears: you can hit their thick end with a hammer without breaking them while a slight pressure applied to their thin end is enough to shatter the entire tear. The properties of safety or even gorilla glass are determined to a large extent by their internal tensile stresses. However, until now, our understanding of the unique characteristics exhibited by the condition of the glass as compared with a tough molten mass was spotty at best. Now, a collaboration of several German and Cretian research teams has offered a surprisingly simple model to explain the difference between glass and molten materials.

The HZB's contribution was by chemist Dr. Miriam Siebenbürger of the Institute for and . Siebenbürger came up with a rather elegant consisting of spherical in aqueous solution (a mixture known as a suspension). Due to the tiny size of the particles – each having a diameter of around 150 nanometer – they float in the but never sediment. The are covered by a thermosensitive "shell", whose thickness can be adjusted by varying the temperature, causing them to shrink and grow reversibly in a continuous manner. This allows the chemist to convert her samples from a densely packaged "glass" into a less dense, more fluid state, in other words melt them down. Through a series of rheological measurements, Miriam Siebenbürger was able to determine how quickly the internal tensions in her samples could relax at different particle packing densities.

For this purpose, she placed the samples in-between two parallel plates, which she counter-rotated relative to each other to produce shearing forces within the sample. After reaching a stationary state of shearing stress at a constant shearing rate, the rotating plates were actively stopped. Next, the force it takes to stop the plates to zero shear rate, and which is a gauge for internal tensions, was measured. In the process, the critical difference between the fluid and glassy state became apparent:

Chemist Dr. Miriam Siebenbürger has contributed to develop a new method to distinguish between a glassy and liquid state. Credit: HZB

Whereas the fluid tensions dissipated without a trace, a proportion of the tensions was maintained in the glassy state. The results are fitting nicely into the theoretical model developed by a group of Constance physicists who calculated the behavior of hard spheres at different packing densities. What's more, measurements of the internal tensile stresses and dynamics of larger-sized particles (in the m range) by Cretian and Düsseldorf researchers and the molecular dynamics simulation of hard spheres by a team of researchers from Cologne and Mainz exhibit similar patterns of behavior. The scientists are convinced that their findings apply to all types of glass that are created as a result of their high packing densities including metallic glass, which is mainly used for high-tech applications. The researchers' findings have now been published in the renowned scientific journal, Physical Review Letters.

Explore further: X-rays reveal coexisting structures in glass

More information: M. Ballauff, J. M. Brader, S. U. Egelhaaf, M. Fuchs, J. Horbach, N. Koumakis, M. Krüger, M. Laurati, K. J. Mutch, G. Petekidis, M. Siebenbürger, Th. Voigtmann, and J. Zausch, "Residual Stresses in Glasses", Phys. Rev. Lett. 110, 215701 (2013). DOI: 10.1103/PhysRevLett.110.215701

Related Stories

X-rays reveal coexisting structures in glass

April 10, 2013

The craft of glassmaking extends way back in time. It was over five-thousand years ago when mankind learned how to make glass. Even prior to this discovery, humans had been using naturally occurring glass for tool making. ...

A new way of making glass

November 9, 2012

(—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 ...

Metallic glass: How nanoscale islands react under strain

May 8, 2013

Quick-cooling molten atoms give metal alloys a glassy, or random, atomic structure that generates higher elasticity and better wear- and corrosion-resistance than their crystalline alloy counterparts. However, these 'metallic ...

Physicists crack another piece of the glass puzzle (w/ Video)

October 16, 2012

(—When it comes to physics, glass lacks transparency. No one has been able to see what's happening at the molecular level as a super-cooled liquid approaches the glass state – until now. Emory University physicists ...

Weird science: Crystals melt when they're cooled

May 23, 2013

( —Growing thin films out of nanoparticles in ordered, crystalline sheets, to make anything from microelectronic components to solar cells, would be a boon for materials researchers, but the physics is tricky because ...

Recommended for you

Shocks in the early universe could be detectable today

October 27, 2016

(—Physicists have discovered a surprising consequence of a widely supported model of the early universe: according to the model, tiny cosmological perturbations produced shocks in the radiation fluid just a fraction ...

Bubble nucleus discovered

October 27, 2016

Research conducted at the National Superconducting Cyclotron Laboratory at Michigan State University has shed new light on the structure of the nucleus, that tiny congregation of protons and neutrons found at the core of ...

Neutrons prove the existence of 'spiral spin-liquid'

October 27, 2016

Magnetic moments ("spins") in magnetic solids are capable of forming the most diverse structures. Some of them are not only of interest from a scientific point of view, but also from a technical standpoint: processors and ...


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.