We demonstrated a mechanochromic chameleon packaging that quantitatively visualizes damage based on the polydiacetylene blue-to-red color transition. The applied pressures on the damage can be conveniently read by taking a photograph via a homemade mobile app called the "Pressure Analysis App". The key aspects of the development were 1) the adjustment of the sensitivity by adding guest molecules into the PDA matrix, 2) quantitative calibration, and 3) the accurate reading of the pressure from RGB images based on the calibration. The force sensitivity of polydiacetylene on cellulose was characterized in the range of 30-100 nN (2.59-8.86 MPa) at the nanoscale by dual friction force/fluorescence microscopy, and in the range of 0.7-2.2 N (0.11-0.35 MPa) at the macroscopic scale by a friction tester. The scanning speed was found to be one of the key parameters, where the force sensitivity above 50 mm/s was 6.45 times larger than that below 10 mm/s. The developed mechanochromic packaging system can be used for transporting electronics and medical tools, such as vaccine vials, food, etc., more safely and reliably in the future.
Keywords: force sensor; friction force microscopy; mechanochromic polymer; polydiacetylene; quantitative calibration.