Mechanochromic and programmable cellulose nanocrystals ionogels for dual-mode ionic skins

The integration of programmable mechanical properties, dynamically tunable structural color and intrinsic ionic conductivity into a single material system remains a significant challenge. Mimicking the adaptive camouflage of chameleons, we report a conductive and mechanochromic ionogel with exceptional flexibility, realized through a robust post-assembly solvent exchange strategy. A hierarchical Bouligand architecture, derived from the cholesteric self-assembly of cellulose nanocrystals (CNCs), serves as a structural scaffold within a polyacrylamide network. The ionic liquids (ILs), acting as internal plasticizers and lubricants, in conjunction with the hierarchical CNC Bouligand architecture, synergistically promote multi-scale energy dissipation, endowing the ionogel with high strength (0.38 MPa), exceptional toughness (900 KJ∙m^-3) and good fatigue resistance. Significantly, the ionogels feature post-synthetic programmability. Mild thermal treatment or aging promotes partial solvation of the CNCs by the ILs, triggering transition of the ionogel from a tough elastomer to an ultraflexible state capable of sustaining strains up to 2400%. Additionally, the ionogel functions as a dual-mode ionic skin, exhibiting a vivid strain-dependent color response with high sensitivity (1.12 nm·%^-1) and reliable electrical sensing across a broad temperature range. This design offers a versatile platform for biomimetic skin-like materials where programmable mechano-optical properties and direct visual feedback are essential.