Large-strain and full-color change photonic crystal films used as mechanochromic strain sensors

Mechanochromic strain sensors based on photonic crystals, which can change structural color upon mechanical deformation, are promising for many applications including health monitoring and damage detection. Here, a large-strain and full-color change photonic crystal film as a mechanochromic strain sensor is reported. The mechanochromic photonic crystal (MPC) film with grating nanostructure is achieved by a fast and low-cost inverted nanoimprint lithography. The film enables bright and reversible color shift in the full visible range as it is stretched up to a large strain, which is proven in strain direction parallel and perpendicular to the grating. It is demonstrated that the MPC film can be used as a mechanochromic strain sensor able to visualize strain evolution and strain range of low carbon steel in tensile test, which brings a significant step toward visualizing strain monitoring.