Natural selection

摘要

With the rising price of oil making any improvement in the efficiency of planes more sought after than ever, the aerospace industry is paying attention to the potential of so-called smart materials. The principle behind these materials - and what makes them smart - is their ability to sense and respond to changes in their environment in a predictable way. The material itself acts as the sensor but also does something about what it has detected. The ideal use would be in creating a plane that can automatically and independently sense and change its shape in response to speed or altitude, components bending themselves to optimise the aerodynamic profile without being triggered from within. And while that is still the stuff of science fiction, the notion is the subject of much research within indsutry and academia. Products using smart materials have been around for decades and range from commonplace gadgets to the cutting edge of scientific research. So the piezoelectric cigarette lighter and glasses that tint themselves in bright sunshine can line up alongside superconductors employed in particle accelerators and the self-actuating composites that could lead to shape-changing aerofoils on planes. However, according to Professor Jeremy Ramsden, chair of nanotechnology at Cranfield University, not all are truly smart; some are merely responsive. It is worth pointing out the distinction, he says. "A good example of a smart material, and one that's been around over 50 years, is viscostatic oil. It has long chain polymers that unfold as the temperature increases to give more lubrication, and fold up again as it gets cold," says Ramsden. As a result the viscosity is constant when temperature changes. The key difference is that the response is in proportion to the changing external environment, rather than simply an on/off reaction like the cigarette lighter.