Maltese and Italian scientists are proposing a novel sandwich-type multilayered structure which may be adjusted to exhibit particular thermal expansion properties and may even shrink rather than expand following a rise in temperature.

The idea is to have a soft material which is surrounded by thin layers of a hard material in a sandwich-like manner. If when heated, the hard material on the outside expands more than the soft core material on the inside, then the soft core will spread out to accommodate the expansion of the thin hard outer layers with the result that the whole system shrinks in the thickness direction when heated.

Their model can predict changes in the thermal expansion coefficient as a result of changes in the constituent materials or changes in the geometric parameters related to the model.

Prof. Joseph N. Grima, the lead scientist on this project from the University of Malta, said this system was not only of interest because of its ability to achieve negative thermal expansion, but more importantly, due to its versatility.

“The main advantage of our work is that it will permit us to design systems which can demonstrate thermal expansion coefficients of any required value, which can be either positive, negative or close to zero.

“This means that we can have a tailor-made response to temperature changes with the result that we may minimise some of the problems that are normally associated with thermal expansion.”

Prof. Gianluca Cicala, the lead engineer from the University of Catania, is confident that the proposed system has excellent potential for manufacture at a large scale and commercialisation.

The urge for films with tailored thermal expansions properties comes mainly from the requirements of the microelectronic and composites industries.

Several applications like ‘land grid array’ for the microelectronics and multilayered systems for composites laminates working in high temperature environments could benefit from the findings of our work.

“For this reason, our simulations were all based on commercial available polymeric systems. This will help us in the practical realization of the device which have been featured,” he said.

This work has been funded by the Malta Council for Science and Technology and the Universities of Malta and Catania.