Mechanochromic Devices for Strain Sensor Applications

In the field of materials science and engineering, materials that respond to stimuli, such as strain or humidity, and materials that are “soft,” or bendable and stretchable, are becoming more commonplace. Mechanochromic devices are a class of technology that change color or transparency properties when under mechanical stress or strain. This phenomenon is largely achieved through changes in the physical surface structure of the device, such as the formation of wrinkles or cracks in the top layer of a multi-layered composite material. For some mechanochromic devices, the composite material is an elastomer substrate topped with two or more layers of rigid films formed from pigments or dyes; the elastomer substrate can also be colored to reduce the number of rigid film layers. By design, mechanochromic devices are soft materials that can bend or stretch. Furthermore, the sensitivity of mechanochromic devices can be controlled via careful design of the device; the method of pre-stretching the substrate before the colored layers are applied can be used to tune the mechanochromic response. Therefore, by controlling the response of mechanochromic devices, mechanochromic devices can be applied as mechanical strain sensors. In a time where many manufacturing fields are moving towards soft technologies, such a strain sensor is appealing. Additionally, due to their relatively facile preparation procedures and conditions, mechanochromic devices can easily be integrated into the design of other soft technologies. The ideal use of the mechanochromic devices in this capacity would be to tune them to change color when a soft technology is being stretched to its point of mechanical failure; this blatant, qualitative indication has the potential to stop users from breaking expensive technology. This has significant implications in fields with materials moving in a soft direction, such as stretchable electronics, which have potential applications in robotics, aerospace, and smart clothing technologies.