Thermochromic and temperature regulation properties of phase change materials derived from polymer composites loaded with VO2 particles

Abstract This research work concerns the development of phase change materials based on poly(ethylene terephthalate) (PET) mixed with vanadium dioxide particles (VO 2 ). Monoclinic VO 2 particles were synthesized via a hydrothermal process followed by modification of the particle surface with a silane coupling agent, namely 3‐(aminopropyl) triethoxysilane (APTES). After that, the metal oxide particles were mixed with PET flakes, derived from used PET bottles, in an internal mixer. In this study, the effects of surface modification and concentrations of VO 2 particles on thermomechanical and optical properties of the composites were investigated. From the DSC results, it was found that the percentage crystallinity of PET increased after loading with VO 2 . This indicates that VO 2 can act as a nucleating agent inducing the crystallization of the PET chains. From the scanning electron microscopy with energy dispersive X‐ray spectroscopy (SEM–EDX) images, better dispersion of VO 2 particles in the PET matrix was noticed when the surface‐modified VO 2 particles were used as a replacement for the normal VO 2 particles. This contributed to the greater percentage of visible light transmittance through the composite sheets. Thermogravimetric analysis (TGA) profiles of both PET and PET/VO 2 specimens are similar, indicating that the VO 2 did not accelerate the thermal decomposition of the PET. When the specimens were exposed to an IR lamp, it was found that the temperature behind the PET/VO 2 sheets dropped when compared to that of the neat PET sheets. Some shrinkage and deformation of the PET/VO 2 specimens were also noticed. The higher the VO 2 loading, the greater the deformation. The effect was ascribed to the fact that the actual temperature was above the critical transition temperature of VO 2 . Consequently, the NIR transmittance was suppressed at the expense of the greater NIR absorbance by the VO 2 phase in the composites. Finally, when the specimens were exposed to solar irradiation at ambient temperature, the temperature underneath the PET/VO 2 specimens became greater than that of the control specimen (the neat PET). The result was discussed in the light of the emissivity of VO 2 at ambient temperature, which is considerably low. Overall, this study demonstrates that PET/VO 2 can exhibit both cooling and warming effects, depending on the ambient temperature in relation to the critical transition temperature ( T c ) of VO 2 .