Fig. 1: Thermochromic antennas for passive thermoregulation composites.

a Self-adaptive thermoregulation composite film concept consisting of infrared thermochromic antennas embedded in a polymer matrix. b Schematic of the fabrication protocol for free-form composites. VO₂ antennas were first synthesized by hydrothermal synthesis in a high-pressure autoclave. The polymer films and coatings shown in the photographs were then respectively made by hot pressing and spray coating. A dedicated photograph with a scalebar of a hot-pressed and spray-coated sample is shown in (d) and Supplementary Fig. 5, respectively. c Scanning electron microscopy (SEM) image of VO₂ antennas, showing the width (\(W\)) and length (\(L\)) size distribution (Methods). d Photograph of composite thermochromic film made by mixing VO₂ antennas with polyethylene (0.55% v/v) and hot-pressed against an aluminum foil. The polymer film composite has a thickness of only \(85\pm 15\,{{\rm{\mu }}}{{\rm{m}}}\) (Supplementary Fig. 4) and is flexible (inset). e Measured hot/cold spectral emissivity of the composite film (solid line). The red and blue filled area correspond to numerical simulations using the refractive index of VO₂ and PE reported elsewhere (Supplementary Fig. 9)^33,40. f Average emissivity in the atmospheric window, during heating and cooling cycles. g Thermal camera images of carbon black (\(\epsilon \approx 1\)), aluminum (\(\epsilon \approx 0\)) and thermochromic composite heated from 40 to 95 °C. The scalebar shows the apparent temperature registered by the camera, where \({T}_{\max }\) corresponds to the heating temperature. The switch at ~70 °C of the composite from a low to a high emissivity state is evident. The variation in color tones for the aluminum foil sample are due to wrinkles on the surface, which cause non-uniform temperature distribution under the thermal camera. Source data are provided as a Source Data file.