A facile photoinitiated polymerisation route for the preparation of photonic elastomers with chiral nematic order

Abstract

Photonic crystal elastomers that can change colour upon stretching or compression have potential applications in mechanical sensors and optical coatings. However, facile synthetic strategies are required for these materials to be made on a commercially viable scale. To address this issue, we report a photoinitiated polymerisation method to prepare stretchable chiral nematic cellulose nanocrystal (CNC) elastomer composites that exhibit reversible visible colour upon the application of mechanical stress. The initial CNC-elastomer composite is colourless, but when it is stretched (or compressed), the helical pitch of the chiral nematic structure is reduced to lengths corresponding to the wavelengths of the visible region, resulting in colouration. By increasing the percentage elongation of the material (ca. 50–300%), the structural colour can be tuned from red to blue. The colour of the material was characterised by reflectance optical spectroscopy and reflectance circular dichroism to confirm the wavelength and polarisation of the reflected light.</p