Elastic gels change colour when exposed to UV light

The gels, developed at North Carolina State University, are impregnated with a type of photochromic compound called spiropyran. Spiropyrans change colour when exposed to UV light and the colour they change into depends on the chemical environment surrounding the material.

The researchers made the gels out of an elastic silicone substance, which can be chemically modified to contain various other chemical compounds — changing the chemical environment inside the material. Changing this interior chemistry allows researchers to fine-tune how the colour of the material changes when exposed to UV light.

’For example, if you want the material to turn yellow when exposed to UV light, you would attach carboxylic acid,’ said Dr Jan Genzer, Celanese professor of chemical and biomolecular engineering at NC State and co-author of a paper describing the research. ’If you want magenta, you’d attach hydroxyl. Mix them together and you get a shade of orange.’

Photochromic compounds are not new, but this is the first time they’ve been incorporated into an elastic material without impairing the material’s elasticity.