An international team of researchers, directed by Professor Tullio Scopigno from the Sapienza Department of Physics, has revealed the effects of ageing on the elastic properties of resins by using an ancient amber fossil found in the recently discovered deposit at El Soplao in Cantabria (Spain).

Amorphous materials such as amber (resins, polymers, glass and ceramics) are metastable, which means they experience an intermediate state between a liquid and a solid, and are subject to slow structural modifications evolving towards more stable configurations over millions of years.

Understanding such “ageing” processes is of fundamental importance in order to define the peculiar nature of amorphous systems which, as Professor Scopigno explains: “are usually synthesized starting from a liquid state through a cooling process that avoids crystallization, namely the formation of a microscopically ordered solid. The typical disordered structure of a liquid is maintained, but with viscosity values levels pertaining to common solids.”

This class of materials is extremely significant from a technological point of view and is widely used in signals transmission (optic fibre), in micro-electronics, opto-electronics and photovoltaic applications (amorphous silicon), as well as for the development of plastics and adhesives. However, to date, most of their physical properties have not yet been fully understood and rationalized as part of an accepted theoretical model. 

The direct observation of the evolution of glass prosperities, in fact, presents a significant achievement: it takes place on extremely long time scale, that are inaccessible to experimental observations. Thus, studies on ageing are normally restricted to theoretical or computational methods. In order to experimentally observe the effects of ageing on the properties of an amorphous system after a geological span of millions of years, the researchers exposed the amber to a specific thermal treatment. It was heated for a certain time above the glass transition temperature and then cooled to room temperature undergoing the conventional vitrification process.

This procedure allowed researchers to bring the fossil to the state in which it was when the process first began, a sort of thermal “lifting” to erase the traces of time and rejuvenate the fossil by 110 million years.

“Comparing the properties of the vitreous amber before and after the thermal treatment that rejuvenated the material, bringing it back to its original state of 110 million years ago,” explains Eva Pogna, first author of the paper, “allowed us to relate for the first time the disorder level in an amorphous material to its age, revealing how its elastic properties have evolved during the stabilization process.”

The study is the outcome of an international collaboration among Sapienza University of Rome, the European Synchrotron Radiation Facility in Grenoble, the Italian National Research Council and the Italian Institute of Technology.

References:

Tracking the Connection between Disorder and Energy Landscape in Glasses Using Geologically Hyperaged Amber - E. A. A. Pogna, A. I. Chumakov, C. Ferrante, M. A. Ramos and T. Scopigno - J. Phys. Chem. Lett., 2019, 10, pp 427–432 Publication Date (Web): January 7, 2019 DOI:10.1021/acs.jpclett.9b00003

For further information

Tullio Scopigno
Department of Physics, Sapienza University
tullio.scopigno@uniroma1.it