Effect of silica nanoshell on the stability and thermochromic properties of monoclinic VO2 particles dispersed in Poly(vinylbutyral) films

Abstract

Belt-shaped particles of the metastable phase vanadium dioxide (VO2(B)) were synthesized via a hydrothermalmethod using ammonium metavanadate and oxalic acid. To be transformed into the thermochromic monoclinicphase (VO2(M)), the particles were annealed at 550◦C. To enhance the stability and optical properties whilepreventing coarsening, a SiO2 nanoshell was grown on the VO2(B) particles using a modified St¨ober method. ThisSiO2 shell protected the particles, preserving their morphology and preventing coarsening. The resulting VO2(M)particles were incorporated into composite films made from PVB, a UV-resistant polymer used in security glass.These films demonstrated excellent transparency and contrast between transmissive and reflective states,attributed to the SiO2 shell’s stabilizing effects. The SiO2-coated before the annealing treatment VO2 particlesalso exhibited improved chemical and thermal stability. These findings show the potentiality of SiO2-coatedVO2(M), as a material to produce laminated protective glass with long-term thermochromic properties.