Ion‐Conducting Photonic Crystal Elastomers for Wearable Body Motion Sensing

Abstract Ion‐conductive photonic crystal elastomers (ic‐PCEs) uniquely combine stimuli‐responsive color changes with electrical feedback, enabling transformative applications in wearable electronics and adaptive camouflage. However, their fabrication methods are limited. Here, a scalable swelling–deswelling approach is presented to fabricate ic‐PCEs by diffusing ionic liquids into pre‐assembled PCEs. When swelling, the polymer matrix is initially dilated to create intermolecular spaces, facilitating homogeneous ionic liquid diffusion. Once diffusion is complete, hydrogen bonding stabilizes the ionic liquid within the matrix, forming a conductive network beyond a threshold concentration. At ∼50 wt% ionic liquid content, the ic‐PCEs exhibit high ionic conductivity (∼0.46 mS cm −1 ) and a ∼55% enhancement in color brightness. The ic‐PCEs are highly stretchable, with a rapid recovery time (∼170 ms) and reversible color and electrical resistance responses to strain. Under 50% strain, the material shows a color shift from red to bluish‐green, a ∼20% decrease in reflection wavelength, and a ∼135% change in electrical resistance. Exceptional thermal stability and durability further ensure reliable performance. The potential of ic‐PCEs as wearable motion sensors applied to fingers and joints is demonstrated, showcasing their multifunctionality. This work provides a robust route for scalable ic‐PCE fabrication, opening new opportunities for advanced wearable devices and adaptive materials.