Self-Regulating VO2 Photonic Pigments

Nanostructured photonic pigments exhibiting structural colors hold promises to replace conventional pigments for several applications. One emerging challenge in the field consists in integrating additional functionalities to the pigments beyond colors. For instance, integrating phase changing materials, such as VO2, would enable the emergence of a new generation of photonic pigments that regulate autonomously the flow of light in the infrared range while conserving their color in the visible range. Yet, developing those self-regulating pigments requires designing VO2 periodic nanostructures and developing a robust and scalable fabrication approach based on low-cost chemical methods. It is well known that synthetizing and shaping vanadium-based compounds in a reliable way represents a longstanding challenge in the domain. Herein, we demonstrate the fabrication of self-regulating photonic pigments made of VO2 micrometric spheres with inverse opal architectures. We developed a chemical route based on the sol–gel process and colloidal self-assembly coupled with high-throughput spray-drying. Importantly, the key to achieve a robust synthetic approach relies on the controlled pseudomorphic transformation between V2O3 and VO2 during thermal annealing. A set of in situ and ex situ microscopy and spectroscopy techniques were used to characterize the VO2 pigment behavior during phase transition in the visible and infrared range, revealing that these pigments modulate IR radiation while maintaining their structural color in the visible region. We demonstrate that these pigments can be easily integrated into paints and coating or embedded into elastomeric objects, opening interesting perspectives for applications in textile or architecture.