Chameleons on Mars

Researchers from Sandia National Laboratories and the University of New Mexico have created intelligent nanostructures that are able to report on their environment by changing colour.

Intelligent nanostructures that report on their environment by changing colour from blue to fluorescent red under mechanical, chemical, or thermal stress have been created by researchers at Sandia National Laboratories and the University of New Mexico.

The self-assembling structures, which are said to be as durable as seashells, may lower costs by reducing the need for expensive manufactured devices like stress detectors, chemical analysers, and thermometers.

The material also can report changes in mechanical stress and temperature. When the environmental disturbance is removed, the structures change back to their original colour.

‘The material is of interest to NASA — one of the sponsors of our research — for a thin film for an inflatable structure that would aid in the inhabitation of Mars,’ said Jeff Brinker, Sandia senior scientist and UNM professor. ‘The structure’s skin would require a very thin yet strong membrane with low permeability that could sense mechanical damage from hazards such as meteorites or sandstorms.’

The Sandia/UNM method is said to be a generic, efficient solution to a problem that has puzzled modern materials science: how to efficiently distribute conjugated polymers within a hard, protective structure.

‘Traditionally, bulk conjugated polymers are like a huge bowl of entangled spaghetti,’ said Brinker. ‘Our method organises this jumble by forcing them to adopt a particular conformation; that is, we organise them into nanostructures. We can force them into conformations, and so define where the polymer is and isn’t. Then we can control how interactions between polymer units will affect a material’s electrical and optical properties.’

A robust architecture that’s optically transparent and prevents oxidative degradation of the polymer can then be patterned on surfaces and substrates.

‘This is a simple means of forcing organisation that should help us integrate conjugated polymers into devices,’ added Brinker.

It is said to take seconds for the Sandia/UNM method to evenly pre-distribute monomers — simpler precursors of polymers — within a silica matrix through self-assembly. Exposure to UV light polymerises the monomers into conjugated polymers housed in nanoscopic channels that penetrate the matrix of the material.

The result is a nanocomposite that is mechanically robust, optically transparent, and produces telltale changes of colour under changing environmental conditions.