Non-close-packed colloidal photonic crystals (CPhCs) are widely employed in biomimetic strain sensors as they exhibit mechanochromism due to changes in the crystal lattice spacing under stress. However, the structural color of a CPhC film with an incompressible polymer matrix changes with modulation of the film thickness due to deformation, which makes it difficult to visualize the magnitude and direction of the stress. To address this limitation, elastic modulus-controlled CPhC films with stress-responsive mechanochromic behavior are fabricated. While each CPhC film shows the same color change under constant strain, the color change is controlled differently under constant stress. Combining CPhC films prepared with different modulus values enhanced the strain-responsive mechanochromic sensitivity by ≈25 times. A mechanically heterogeneous weave structure demonstrates a unique biaxial mechanochromic response based on the direction of the stress. These findings suggest that CPhC films can serve as versatile strain/stress sensors that provide visual information about the magnitude and direction of applied stress in multiple dimensions.
This research was financially supported by the Institute of Civil\\u2010Military Technology Cooperation funded by the Defense Acquisition Program Administration and the Ministry of Trade, Industry, and Energy of the Korean government under grant No.22\\u2010CM\\u2010CO\\u201001. This work was also supported by the Ministry of Education of the Republic of Korea and the National Research Foundation of Korea (no. NRF\\u20102017R1A5A1015365, NRF\\u20102022R1F1A1065195).
