Responsive structural color materials for sensing strain, water, and camouflage

Chameleon skins capable of dynamically adjusting and reversibly turning on-off their structural colors have attracted great interest. However, most chameleon-inspired responsive structural color materials (RSCMs) can only mimic the dynamic color and show poor stability, stretchability (strain <68 %), and responsive speed (< 1 nm/ms), significantly restricting their practical applications. Here, force/water-responsive RSCMs that can independently imitate dynamic and on-off structural colors have been fabricated by 1) non-close-assembling silica particles into the 4-hydroxybutyl acrylate (HBA) to generate swellable hydrophilic photonic crystals (PCs), 2) swelling the PCs by HBA, and 3) photopolymerizing swelled PCs. Compared to traditional RSCMs, the RSCMs possess no solvent and super-large lattice distances with a high elastic modulus, resulting in outstanding stability and mechanochromism, involving large strain (0-110 %), large Δλ (253 nm), ultrafast responsiveness (6.7 nm/ms), and excellent reversibility (> 500 times). Moreover, the RSCMs exhibit an unconventional water-responsiveness of reversibly turning on-off color under the dry-water states, due to the refraction mismatching-matching. RSCMs-based trip-mode camouflage was realized, showing their great potential in wireless sensing, optical devices, anticounterfeiting, etc.