Single and Double Microencapsulation of Organic Thermochromic Material
Authors: Nagare Sushant M. , Hakami Abdullatif , Stefanakos Elias K. , Srinivasan Sesha S. 
Published: October 2024

With the increase in temperature, urban areas face issues like urban heat islands. The reduction of green vegetation across urban areas has led to a tremendous rise in temperature. Many studies suggest significant cities are currently experiencing this issue to a greater extent. Many researchers are working on building paints and dyes to reduce the heat intake of the building. Organic thermochromic materials are one such alternative for building dye and stain. The main issue with using organic thermochromic materials is that they quickly degrade under sunlight, which makes them less useful for building paint. To overcome this issue, many organic thermochromic black dye materials (OTCBDM) are encapsulated with inorganic materials such as metal oxide, which block sunlight and reduce the effect of degradation. Encapsulation is achieved via the emulsification method of metal oxide. This paper deals with the single and double microencapsulation methods with different surfactant concentrations, metal oxides, and combinations thereof. Various techniques were used such as Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) with energy‐dispersive X‐ray spectroscopy technique (EDS), and differential scanning calorimeter (DSC), UV‐Vis spectroscopy, thermogravimetric analysis (TGA), and CIE Lab space analysis to determine the materials’ encapsulation and chromatic nature. The FTIR spectra suggested the absorption peaks for the Ti─OH bond (at 814, 903, and 913 cm−1) and Si─OH group (at 1,084 and 1,178 cm−1) for the commercial dye encapsulated with TiO2 and SiO2. The Ti─O─Si bonds at 1,054 and 1,145 cm−1 showed for the double encapsulation of SiO2 and TiO2 either (i) doped or in (ii) layered structures. From the EDS analysis, we can clearly say that the presence of SiO2 and TiO2 indicates the encapsulation of the commercial thermochromic black dye material. The SEM micrographs of the TiO2 encapsulation of OTCBDM seem more promising and uniform core–shell structure formation with CTAB as a surfactant than the SDBS. Moreover, the SEM microstructure results of double encapsulation using both TiO2 and SiO2 suggested thicker coating of particles when compared with single encapsulated counterparts. The cold phase of layered double encapsulation of OTCBDM + SiO2/TiO2 shows a darker color than the doped combination as obtained from the CIE Lab results. This feature suggested that an efficient encapsulation and chromatic transition are achieved in a layered combination of double encapsulation than in a doped combination. The DSC spectra indicated the increase in enthalpy at the heat cycle from 94.147 J/g for the SiO2 microencapsulated OTCBDM sample compared to all other samples shows thermal energy storage behavior for outdoor building applications. The UV–Vis absorbance spectra show two distinct peaks at 470 and at 610 nm related to the OTCBDM. The single‐layer encapsulated organic thermochromic black dye material shows less absorbance compared to the plain organic thermochromic black dye material. The double encapsulated sample has the highest absorbance compared to all other samples suggesting the material having better retention of peaks at 470 and at 610 nm. The thermographic analysis (TGA) shows when compared to the plain and single encapsulated OTCBDM samples, the double encapsulated samples demonstrated higher thermal endurance characteristics due to thicker layer coatings of the shell over the core structure. The novelty of this work relies on the double encapsulation of OTCBDMs using SiO2 and TiO2 to improve the photodegradation behavior of the organic core dye particles, and we have demonstrated that the cationic surfactant CTAB outperforms than the SDBS in microencapsulation processes.