Multifunctional nylon filaments for simultaneous ultra-violet light and strain sensing

Webbings are critical load-bearing components that are frequently exposed to severe environments. To date, sensing techniques for applied strain and ultra-violet (UV) irradiation on webbings are still lacking. Here, we put forward a class of multifunctional filaments to bridge this technical gap. Multifunctional filaments are fabricated by attaching functional materials to the filaments ' surfaces through a pressurized coating process. UV-sensitivity is accomplished by a layer of photochromic materials coated on the filament. Upon UV irradiation, the photochromic filaments demonstrate a rich color variation that could support UV sensing. The optical responses of the photochromic filaments are elucidated by a mathematical model based on the photochemistry of the underlying chemical reactions. Strain-sensitivity is realized by a layer of photonic crystals coated on the filament. An applied strain modulates the closely packed nano-structures of the photonic crystals, leading to a shift in the filament color. We demonstrate that by incorporating photochromic materials and photonic crystals on the same filament, it is possible to accomplish simultaneous UV and strain sensing. The proposed filaments could be embedded in webbings to enable noninvasive monitoring of their integrity.