Mechanically Tunable Mechanochromic Device with Covert‐Overt Structural Color and Modulation of its Transparency

In this study, A novel mechanically responsive optical device (MROD) is introduced which is capable of modulating light transmission and produces iridescent structural colors under reflection. This device is facilely constructed by embedding a reflowed monolayer of poly(methyl methacrylate) (PMMA) nanoparticles beneath the surface of commercial tape. Due to the minimal refractive index contrast between PMMA and the tape, the nanoparticles remain optically invisible at the resting state. However, when the tape is stretched, the nanoparticles are extruded out of the surface and work as scattering centers in transmission mode or as a photonic crystal in reflection mode. By regulating the applied stretching force, the transmittance (30–89%) and reflected color can be precisely controlled. The optical transition is driven by the exposure of the nanoparticles under tension, which are originally concealed beneath the surface. Additionally, the fabrication process is cost‐effective and scalable, making this principle highly promising for applications in anti‐counterfeiting labels, colorimetric sensors, optical modulator, and indicators.