Washington, Oct 5 : With its history dating back to 5,000 years, the nature of glass is still a mystery to scientists. Now, a professor of chemical engineering at the University of Delaware claims that he knows why glassy materials make the transition from a molten state to a solid.
Archaeological evidence suggests that glass was first made in the Middle East sometime around 3000 B.C.
According to Richard Wool, what distinguishes glasses from other materials is that even after hardening, they retain the molecular disorder of a liquid. In contrast, other liquids, for example water - assume an ordered crystal pattern when they harden.
Glass does not undergo such a neat phase transition; rather, the molecules simply slow down gradually until they are stuck in an odd state somewhere between a liquid and a solid.
In a paper to be published later this year in the Journal of Polymer Science Part B: Polymer Physics, Wool documents a new conceptual approach, known as the Twinkling Fractal Theory (TFT), to understanding the nature and structure of the glass transition in amorphous materials.
The theory provides a quantitative way of describing a phenomenon that was previously explained from a strictly empirical perspective.
"The TFT enables a number of predictions of universal behavior to be made about glassy materials of all sorts, including polymers, metals and ceramics," Wool says.
Another difference between glasses and more conventional materials is that their transition from the liquid to the solid state does not occur at a standard temperature, like that of water to ice, but instead is rate-dependent: the more rapid the cooling, the higher the glass transition temperature.
Wool discovered that as a liquid cools toward the glassy state, the atoms form clusters that eventually become stable and percolate near the glass transition temperature. he percolating clusters are stable fractals, or structures with irregular or fragmented shapes.
"At the glass transition temperature, these fractals appear to twinkle in a specific frequency spectrum. The twinkling frequencies determine the kinetics of the glass transition temperature and the dynamics of the glassy state," the expert added.