Brilliant Mechanochromic Scattering Structural Colors

Conventional mechanochromic photonic crystals (MPCs) have attracted broad interest because of their force-adjustable reflective structural colors, which require three-dimensional and nonclose-packing structures. Here, a new type of MPC with monolayer close-packing structures, brilliant iridescent scattering structural colors, and unconventional mechanochromic properties has been fabricated by self-assembling ZnS particles into a layer of polycrystalline structures and then infiltrating interparticle gaps with elastic polyurethane (PU). The scattering light diffracted in the forward direction and high diffraction efficiency by the large refractive index contrast between ZnS particles and PU contributes to a high scattering color saturation. The MPC shows interesting mechanochromic scattering structural colors with the color red-shifted and blue-shifted along and perpendicular to the stretching directions, originating from the unique crystal orientation-dependent deformation. This work upgrades the basic understanding of the relationship between structures and optical properties and offers a perspective for designing advanced stimulus-responsive photonic materials.