October 17, 2012
Cracked Up – Molecular Movement Of Glass Particles Studied
[ Watch the Video: Brownian Diffusion of a Colloidal Tetrahedral Cluster ]
Scientists are insatiable people. Their never-ending quest to know the “how” and “why” of every little thing has brought us where we are today. As a result of tireless research, scientists have found a way to deliver robotic rovers into space, what materials are more conducive to the transference of data, and what happens when you dip a banana in a vat of liquid nitrogen.
Yet, for all their Eureka moments, they´ve yet to figure out a material which many of us take so much for granted that we often just look right through it: Glass.
The transformation of water to ice is well enough understood. As the temperature drops, the water molecules begin to slow down until they´re eventually locked into a crystalline formation, somewhere around the 32 degrees Fahrenheit area.
Now, a group of physicists from Emory University have put together a movie displaying the molecular movement of glass particles and have discovered that, unlike glass, these molecules slow down at low temperatures but never lock into a crystalline formation.
Scientists have never been able to watch these molecules shift and move into their glassy form until now, and this video could be a first step in finally cracking this code.
These Emory physicists conducted their research in Eric Weeks´ lab and will be publishing their findings in the Proceedings of the National Academy of the Sciences.
“Cooling a glass from a liquid into a highly viscous state fundamentally changes the nature of particle diffusion,” explained Weeks on the Emory University Web site.
“We have provided the first direct observation of how the particles move and tumble through space during this transition, a key piece to a major puzzle in condensed matter physics.”
According to this new data, the molecules in glass only become more viscous and “glassier” as the temperature drops. Though scientists can finally observe this behavior, they´ve yet to understand why.
After observing this data, these scientists are now wondering if glass is really a solid at all, or just a very, very slow moving liquid. Hundreds of years ago, some noticed glass panes tended to be thicker on the bottom than the top and assumed that glass merely fell with the passing of time.
Weeks is quick to dispel this myth, saying the real reason glass panes are thicker on the bottom is because glass makers at that time had yet to figure out how to make a truly flat plane.
“For practical purposes, glass is a solid and it will not flow, even over centuries. But there is a kernel of truth in this urban legend: Glasses are different than other solid materials."
In order for Weeks and his team to recreate the movement of glass molecules for videotaping, they used a mixture of water and small, plastic balls to represent the molecules, each nearly the size of the nucleus of a cell. When the concentration of these particles is increased, this model reacts in a way similar to glass.
The only problem with the model, however, is the spherical shape of both water and the plastic balls. According to Weeks, glass molecules are quite irregular in shape.
“We wanted to set up an experiment that would allow us to see that movement, but spheres move differently than irregular shapes,” said weeks. When these molecules do begin to move, Weeks likens their movement to a pack of gridlocked cars trying to break free from the group.
“You can´t turn your car around, because it´s not a sphere shape and you would bump into your neighbors. You have to wait until a car in front of you moves, and then you can drive a bit in that direction. This is directional movement, and if you can make a bunch of these, you may eventually be able to turn your car. But turning in a crowded parking lot is still much harder than moving in a straight line,” explained Weeks.
With this model in place, Weeks hopes he and his fellow scientists and physicists can finally make some progress in understanding this material which is progressively becoming more important to a society in love with their smartphones and tablets.