Adjustable Thermal Shrinkage

Groundbreaking work published this week in the ‘Proceedings of the Royal Society A’ by an academic from the Faculty of Science of the University of Malta and his research team is making headlines in the international scientific press. So much so, that it is being reported as breaking news by ‘New Scientist.com’, the website of New Scientist, which is cited as the World's No.1 Science & Technology News Service. On this website, a global network of specialist correspondents promote important scientific discoveries which are likely to have a significant impact on society.

The team of University of Malta scientists led by Dr Joseph N. Grima and colleagues Pierre-Sandre Farrugia, Ruben Gatt and Victor Zammit have developed a way of designing structures, of any size, that shrink when heated (negative thermal expansion). Their work, funded by the Malta Council for Science and Technology (MCST) and CHISMACOMB (an EU FP6 project), can be extremely useful in reducing the impact of thermal expansion on anything from bridges to microscopic systems.

"The University of Malta is gradually building an infrastructure to conduct world-class research in niche areas of engineering, science and medicine. Though we do not have a long standing tradition of institutional research, and despite the very modest funds to sustain such endeavors, our up and coming researchers have shown, time and again, through their publications, that they can put us on the international map of scientific and technological innovation. Indeed, I am thrilled to see some of the work of the University of Malta being given such prominence in the Proceedings of the Royal Society and by New Scientist. I am sure that with the right investment and nurturing we will see Malta grow in profile in research which is an indispensable cornerstone of our emerging knowledge-based economy." said Prof. Camilleri, the Rector of the University of Malta.

"This is a notable achievement in Research and Innovation in Malta", stated Mr. David Spiteri Gingell, Chairman, MCST, "that proves that Maltese researchers have the potential to compete with the best on a European and Global level. The RTDI Programme is one of the thrusts to unlock such hidden potential." The Project was partly funded by the National Research Technological Development and Innovation (RTDI) Programme launched in 2004 by the MCST. The National RTDI Programme aimed at stimulating and building a culture for sustained scientific research and innovation activity by providing financial support for scientific research, ranging from basic and applied research to near-to-market innovation.

The University of Malta team studied triangles with at least one side made from a different material to the others, connected by rotating joints. If the diverse materials change volume in response to temperature in a different way, the triangles may actually shrink in one direction when heated. They derived equations which describe the behaviour of their triangle-framework system and these are essential to predict the response to temperature of their structure, which can be constructed at any scale. In other words, their mathematical model makes it possible to choose exactly how such a structure behaves. For example, they show that if one side of a triangle is more responsive to heating, it will stretch the other two wider, drawing the point opposite closer, thus resulting in a shrinkage in the height of the triangle.

See http://home.um.edu.mt/auxetic/nte.gif where an animation shows how a part of the framework behaves as temperature changes - the red struts respond to temperature more than the others.

Dr Grima and his colleagues think lattices of such triangles could have all kinds of applications. "We have shown that it is possible to easily design systems which exhibit a tailor-made response to temperature" says Grima, "These systems can be constructed very cheaply and can be as big as a bridge or on a microscopic scale." By virtue of its construction, this structure should be able to bear loads without problems, he adds. The team is starting to experiment with real frameworks to see how they perform. Grima’s team of scientists is also interested in more complex materials. "By incorporating such a rigid framework into another softer material – like rubber – you could create a ‘solid’ with these anomalous thermal properties," says Grima.

Grima also works on auxetic materials (negative Poisson’s ratio), which thanks to their geometric frameworks can expand when stretched, instead of getting thinner. "One of our aims is to combine the two concepts together to produce systems that have both properties simultaneously negative. This could have some very interesting consequences, such as in the manufacture of high-performance tunable filters where the pore sizes could be made bigger by stretching or smaller by heating".

This is not the first time that academics from the Faculty of Science are reporting such groundbreaking news in the proceedings of the Royal Society. In fact, more than a century ago Professor Sir Temi Zammit, the first Dean of the Faculty of Science, had published in Proc. Roy. Soc. B. his famous note ‘A Preliminary Note on the Susceptibility of Goats to Malta Fever’.

Further information: http://home.um.edu.mt/auxetic/nte.html
Email joseph.grima@um.edu.mt