Polymeric Photonic Crystal Platform with Shape-Memory and Mechanochromic Properties

Smart polymeric materials that visualize, store, and erase mechanical deformation are promising for structural monitoring and deformation-history sensing. Here, we present a polymeric photonic crystal platform combining shape-memory behavior with mechanochromic responses. Core–interlayer–shell colloidal particles, composed of a rigid core, an anchoring interlayer, and a tunable shell, were assembled into non-close-packed photonic crystal films by melt-shear processing. During assembly, the shells formed a continuous matrix, while the arranged cores generated structural color through refractive-index contrast. Mechanical deformation changed the interparticle spacing and shifted the reflection wavelength, enabling strain visualization through color. The polymer shell acted as the switching phase for shape-memory behavior. Its glass-transition temperature and viscoelastic relaxation were controlled by monomer composition, allowing the operating temperature and recovery kinetics to be tuned. When the film was deformed above its transition temperature and cooled, both the temporary shape and structural color were fixed. The color remained after unloading, allowing deformation to be recorded and stored. Reheating near the transition temperature activated polymer-chain mobility and released the stored elastic force, restoring the original shape and optical state. The films showed shape fixation and approximately 92% shape recovery. Time-dependent recovery at different temperatures was analyzed using time–temperature superposition, enabling prediction of long-term behavior and revealing the effects of relative temperature and thermal history. By varying shell composition, modulus, transition temperature, and interfacial design, the platform can be extended to diverse polymer systems and operating ranges.