Shape- and Color-Switchable Polyurethane Thermochromic Actuators Based on Metal-Containing Ionic Liquids

Many creatures have excellent control over their form, color, and morphology, allowing them to respond to the interaction of environmental stimuli better. Here, the bioinspired synergistic shape-color-switchable actuators based on thermally induced shape-memory triethanolamine cross-linked polyurethane (TEAPU) and thermochromic ionic liquids (ILs) were prepared. The thermochromic ILs with various metalized anions, including bis(1-butyl-3-methylimidazolium) tetrachloro nickelate ([Bmim]₂[NiCl₄]) and bis(1-butyl-3-methylimidazolium) tetrachloride cobalt ([Bmim]₂[CoCl₄]), are investigated. The actuators exhibit thermochromic response, as evidenced by a shift in the color of the composites, which is due to the formation of the tetrahedral complex MCl₄^2- (M = Ni and Co) after dehydration. The shape-color-switchable thermochromic actuators have strong molecular interaction between TEAPU and ILs and can mimic natural flowers and change the color and shape quickly in a narrow temperature range (30-70 °C). In addition, these thermochromic actuators can lift more than 50 times their weight and withstand strains of more than 1100%. The results represent the potential application in artificial muscle actuators and intelligent camouflages.