3D-Helical Artificial Chromatophore for Thermally Tunable Fluorescence and Stealth Switching

This paper presents a bioinspired thermochromic actuator that mimics natural camouflage systems by switching between visible and stealth modes in response to temperature changes. Thus, the innovation of this research involves a yarn-based artificial muscle with a helical structure that enables rapid switching between visible and stealth modes through vertical contraction and expansion. Unlike previous systems that rely on mechanical stimuli, this design uses thermal energy to trigger dynamic color changes. Selective surface coating with rhodamine B and titanium dioxide (TiO₂) enables differential photoreactivity to ultraviolet-visible (UV-vis) light and forms the basis for rapid and reversible chromatic transitions. When exposed to an external thermal impulse, the artificial chromatophore─measuring 1400 μm in thickness (outer diameter, OD)─can rotate up to 309°, exhibit a negative strain of 84.6%, and reach a maximum average actuation velocity rate of 297.4 μm/s/°C (Spring Index, SI: 4.6). This performance is among the fastest reported for color-tunable materials. Notably, the system's thermally induced color change is effective not only in air but also in completely different environments, maintaining its performance underwater despite the high thermal conductivity of water. Such an approach is expected to broaden the application of adaptive materials in diverse industries, including space and deep-sea sensors, military stealth and adaptive camouflage, temperature-regulating smart textiles for nighttime use, and smart ocean buoys.