Dynamic Mechanochromic Optics with Tunable Strain Sensitivity for Strain-Responsive Digit Display

A facile but highly effective mechanochromism design is reported that is based on a bilayer structure consisting of a sputter-coated metal light-shielding layer atop a polydimethylsiloxane (PDMS) substrate containing a fluorescent dye, featuring transverse and/or longitudinal microscale cracks when stretched. The crack opening width on the light-shielding layer upon stretching/releasing allows the UV radiation to activate the fluorescent dye in the PDMS matrix to exhibit luminescent color, which can be easily tuned with choice of fluorescent dyes. The strain response of the crack opening width can be fine-tuned by applying various degrees of prestretching strain in the preparation process, resulting in customizable mechanochromic responses. Three types of mechanochromic devices are prepared as representative examples. The fluorescence intensity of these devices can be tuned to either increase or decrease with an increasing strain, or first decrease and then increase within the operating strain range. Moreover, this system can be further modified into a dynamic strain sensor with digit display function, allowing the strain degree of the device to be directly read. This design strategy can be easily adopted by fellow researchers and is expected to open a brand-new avenue to tune mechanochromic response for various dynamic adaptive optics.