Combined Stealth : Thermoactive nanotextured coatings for passive control of surface emittance – MAGIC

Modification of the interaction properties of a material with infrared (IR) radiation can be exploited for dual purposes. Indeed, by working on the IR absorption and reflection characteristics of a material, it is possible to:
- take advantage of solar IR radiation to impact thermal comfort and indirectly reduce energy consumption related to heating or cooling
- optimize discretion in night conditions (night vision (near IR) and thermal camera (thermal IR)).
The aim of the MAGIC project is to combine a "smart material" component and a "functional surface" component in order to develop coatings with a controlled variable emittance. In other words, the aim of the MAGIC project is to combine a thermoactive paint coating with surface nano-texturing. The purpose of the thermoactive paint will be to modulate the apparent temperature of the object according to the thermal operational conditions. The nano-texturing will make it possible to generate materials having different emittances, and therefore different apparent temperatures.
It should be noted that both the coating technology and the nano-texturing of the surface are techniques that can be preformed in large sacles and applied on a wide range of materials (metals, plastics, composites, ceramics and textiles)
The chosen materials and technologies are, on the one hand, Vanadium dioxide (VO2) as a thermoactive agent and on the other hand nano-texturing by femtosecond laser. The thermoactive paint will be made by inserting VO2 particles in a polymer matrix which will then be nano-textured.
The thermoactive properties of a composite paint containing vanadium oxide particles. The VO2 is a "smart material" called thermochromic, i.e. its optical properties change with temperature. Below 67 ° C, the VO2 is a dielectric, it is transparent to infrared radiation so the IR wavelengths are transmitted across the material. The layer containing the VO2 behaves like a neutral layer, allowing the sunlight to heat the substrate. Above, the VO2 particles are in their metallic state and thus reflect the sunlight, thus preventing its absorption and its conversion into thermal energy inside the substrate. The VO2 also has the particularity to undergo a strong modification (about 40%) of its IR emissivity during this change of state, making it possible to use it for stealth technologies.
The particular electromagnetic behavior of a micro or nano-textured surface. Roughly, the surface micro / nano-roughness will modify the interaction between the incident waves and the surface by deflecting them in multiple directions, thus modifying the reflected signal. This micro / nano-texturing will thus allow to mimic the optical behavior of another material (a metal can thus mimic snow or gravel). More precisely, the surface micro / nano-texturing will make it possible to strongly modify the emitance of the material.