Adhesive photonic-ionic skins for visualizing wearable strain distributions

Photonic-ionic skins (PI-skins) inspired by natural skins with ion transduction and chromotropic traits have attracted tremendous attention. Although PI-skins with multiple signal synergistic outputs have been developed, incorporating strong adhesion for direct wearing and precise location of deformation remains highly desirable and challenging. Herein, a mechanochromic and electromechanical PI-skin with superior adhesion, sensitivity, stability, and self-healing ability is presented to visualize wearable strain distributions and monitor human motions. The PI-skin is constructed by integrating a close-packed carboxylated polystyrene (PS-COOH) colloidal array with polymerized deep eutectic solvent (PDES) via in-situ photopolymerization. The as-prepared PI-skin simultaneously exhibits sensitive dual-signal sensing of strain (gauge factor: 1.28, response time: 240 ms, mechanochromic sensitivity of 1.87 nm per percent strain) via adjusting the lattice spacing of the colloidal photonic arrays and resistance. Notably, thanks to the multiple hydrogen bond network of PDES, PI-skin has achieved remarkable adhesion (∼1.44 MPa on glass), mechanical strength, and self-healing performance. Furthermore, the excellent resilience of PDES endows the PI-skin with long-term electrical stability and reproducibility. The PDES contributed to high stretchability (∼1197.8 %), guaranteeing the application as a flexible sensor. The PI-skin promises direct and firm wearing as an interactive sensor for motion monitoring and visual mapping strain distribution.