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‘Rugby ball’ peep into glass

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G.S. MUDUR Published 14.10.14, 12:00 AM

New Delhi, Oct. 13: Using microscopic particles shaped like rugby balls, Indian physicists have provided deep insights into the formation of glass which has remained a mystery in materials science despite its antiquity, ubiquity and utility.

The researchers at the Jawaharlal Nehru Centre for Advanced Scientific Research and the Indian Institute of Science, Bangalore, have through experimental observations of these tiny rugby balls studied the transition that turns liquid material into glass.

Humans have used glass for over 5,000 years, its production evolving from backyard activities in ancient Egypt to the present-day global glass industry with an estimated $75 billion annual revenue that churns out a diversity of products — from windscreens to crystal art glass to wine glasses.

“But the basic principles of how glass forms is still a mystery,” said Ajay Sood, a professor of physics at the IISc. “Glass and liquids have similar atomic arrangements, but their behaviour is completely different — liquids flow, but we never see glass flowing.”

Microscopic studies of glass have shown that atoms and molecules are arranged in a disordered fashion similar to what is observed in liquids — and quite unlike the periodic and ordered arrangement of atoms and molecules that make up crystalline solids.

The puzzle hasn’t held back the glass industry in any way.

The global glass industry generates about $75 billion in annual revenue, with China, France, Germany, Japan and the US as top exporters, First Research, a US-based market analysis agency, estimated in a report updated this year.

Silica is the core component of all glasses, with a number of additional materials, depending on the properties of the glass to be made. A typical glass-making process involves cooling a hot liquid by hundreds of degrees within seconds.

Scientists believe a better understanding of the fundamental principles of glass formation will allow them to tailor properties of glass to improve desired properties.

Serious scientific discussions about the transition of glass emerged during the 1950s and independent research groups have proposed two competing theories.

Peter Guy Wolynes, a professor of chemistry at Rice University in the US, and his co-workers have suggested that glass formation is a thermodynamic phase transition, similar to the transformation of water into ice.

But David Chandler at the University of California, Berkeley, and his colleagues have argued that glass formation involves a process called dynamical facilitation in which atoms and molecules that make up glass relax under the influence of their own highly mobile neighbours.

The Bangalore researchers say scientific debates on the subject have been acrimonious. “The problem was that no one has ever observed atoms and molecules in glass during its exact moment of formation — it’s never been done,” said Sood.

Sood, collaborating with physicist Rajesh Ganapathy at the JNCASR and their students Chandan Mishra, Hima Nagamanasa and Shreyas Gokhale used tiny silica particles shaped like rugby balls and observed their behaviour in laboratory experiments that simulated the formation of glass.

Their rugby balls allowed them to peep into what might happen during glass formation. Their studies support the theory of dynamical facilitation. The results of the Bangalore study appeared today in the US journal Proceedings of the National Academy of Sciences.

“Dynamical facilitation seems to capture many aspects of glass formation, but one set of experiments isn’t going to resolve a 60-year debate,” Ganapathy said. “But we now have a system that can test both theories in the laboratory.”

The researchers speculate that experiments that simultaneously address both the dynamical facilitation and thermodynamic transition theories will be essential to unravel the mystery.

Chandler, who is familiar with the JNCASR-IISc work, said the findings appear convincing. “It is gratifying to me to see how well the analysis we had developed applies to this system,” he wrote in an email sent to the Bangalore researchers.

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