A local high technology materials development company, Peratech, has invented a new type of metal-polymer, named "QTC" (Quantum Tunnelling Composite). This unique material displays very large changes in electrical conductivity when mechanically deformed in any way (ie: compressed, stretched etc). The reason for this unusual electrical behaviour is thought to be due to a quantum-mechanical tunnelling process, whereby conduction electrons tunnel from one metallic grain to another.

Historical (notes added February 2010)

In 1996 David Lussey approached Prof. David Bloor via Knowledge House, which provided an interface between academia and industry in the North East, with an electrically conductive, metal-polymer composite that he had discovered and thought had unusual properties. Prof. Bloor's initial measurements revealed this was the case laying the foundation for on-going research collaboration. This research is unusual as it is the result of the "spinning-in" to the Department of a novel material, which did not conform to accepted physical models. The Department's role has, therefore, been one of providing scientific expertise and experimentation to provide a proper understanding of the physics of the material as a foundation for the development of parallel commercial activity. This has played an important part in the growth of the company (Peratech Ltd) founded by David Lussey to exploit the unique properties of the composite, which has applications in areas associated with touch sensitivity and human interaction with screens, keyboards, controls and switches as well as robotics, security and medicine. A percolation model was used to describe metal polymer composites with the conductivity rising at the percolation threshold when there are enough metal particles to form chains in intimate contact and provide conductive paths spanning the material. As metal content is increased the conductivity increases rapidly across a narrow concentration range as more percolation paths form until saturation is approached when the conductivity rises slowly to its maximum value. David Lussey's composite, loaded above the percolation threshold with Ni powder, should have been conductive but was insulating until deformed. It became conductive when not only when compressed but also when stretched or bent. Our studies revealed that the silicone elastomer matrix intimately coated the Ni particles, which retained sharp surface features with nanometre dimensions¹. Electrical charge residing on the Ni particles produces very large electric fields at the tips of the surface features facilitating electron tunnelling through the relatively thick, adhering, insulating polymer. Deformation reduces the barrier thicknesses and gives rise to large changes in sample resistance, a reduction greater than 10¹⁴ has been observed in compression². The underlying physics resulted in the material being called Quantum Tunnelling Composite (QTC). Peratech has grown strongly over the last five years and developed a variety of conductive composites tailored to clients' specific end uses. Recently Samsung and Nissha Printing have started using printable forms of the composites in mass-market products and this is providing licensing revenues to Peratech amounting to almost £1million in the first year. Research utilising the Department's state of the art facilities now focuses on the new generations of Peratech's composites. On its part Peratech participates in the Department's teaching providing materials and manpower to support B.Sc. Team Projects, M.Sci. final year experimental projects and giving lectures on the company's activities.

References

1. D. Bloor, K. Donnelly, P.J. Hands, P. Laughlin and D. Lussey, A metal-polymer composite with unusual properties, J. Phys. D: Appl. Phys., 38, 2851 (2005). (Included in the top 20 papers in this Journal during 2005)
2. D. Bloor, A. Graham, E.J. Williams, P.J. Laughlin and D. Lussey, Metal-polymer composite with nanostructured filler particles and amplified physical properties, Appl. Phys. Lett., 88, 102103 (2006). (Appeared in the online Virtual Journal of Nanoscale Science and Technology, 13, Issue 11 (2006))

Scanning electron microscope (SEM) images of metal powder used in QTC.

David Lussey, MD of Peratech Ltd. demonstrating the QTC fabric, 'roll-up' keyboard.

An example of where QTC fabrics can be woven into clothing. The jacket sleeve features a control panel for the operation of a personal stereo.