The chameleon effect

Colourful cellulose: The Empa logo 3D-printed from the new HPC mixture changes color when it gets warmer. Image: Empa Is it possible to 3D print biodegradable sensors and displays? Researchers from Empa's Cellulose & Wood Materials laboratory have developed a cellulose-based material that allows just that. The mixture of hydroxpropyl cellulose with water, carbon nanotubes and cellulose nanofibrils changes color when heated or stretched - without the addition of any pigments. An elastic material that changes color, conducts electricity, can be 3D printed and is also biodegradable? That is not just scientific wishful thinking: researchers from the Cellulose & Wood Materials laboratory in Dübendorf have produced a material with these exact properties on the basis of cellulose and carbon nanotubes. The researchers started with hydroxypropyl cellulose (HPC), which is commonly used as an excipient in pharmaceuticals, cosmetics and foodstuffs, among other things. When mixed with water HPC is known to form liquid crystals. These crystals have a remarkable property: Depending on their structure - which itself depends on the concentration of HPC, among other things - they shimmer in different colors, although they themselves have no color or pigment.