The preparation of a plasmonically resonant VO2 thermochromic pigment.

Vanadium dioxide (VO(2)) undergoes a reversible metal-insulator transition, normally at approximately 68 degrees C. While the properties of continuous semi-transparent coatings of VO(2) are well known, there is far less information available concerning the potential use of discrete VO(2) nanoparticles as a thermochromic pigment in opaque coatings. Individual VO(2) nanoparticles undergo a localized plasmon resonance with near-infrared light at about 1100 nm and this resonance can be switched on and off by simply varying the temperature of the system. Therefore, incorporation of VO(2) nanoparticles into a coating system imbues the coating with the ability to self-adaptively modulate its own absorptive efficiency in the near-infrared. Here we examine the magnitude and control of this phenomenon. Prototype coatings are described, made using VO(2) powder produced by an improved process. The materials are characterized using calorimetry, x-ray diffraction, high-resolution scanning electron microscopy, transmission electron microscopy, and by measurement of optical properties.