Microencapsulation of Three-Component Thermochromic System for Reversible Color Change and Thermal Energy Storage
In this study, poly(methyl methacrylate)/thermochromic system (PMMA/TS) and poly(methyl methacrylate-comethacrylic acid)/thermochromic system (P(MMA-co-MA)/TS) microcapsules were prepared by using emulsion polymerization method. The thermochromic system was consisting of crystal violet lactone (CVL) as a leuco dye, bisphenol-A (BPA) as a color developer, and 1-tetradecanol (TD) as a solvent. Microcapsules with different ratio of core/shell were synthesized to examine the effect of core/shell ratio on the properties of microcapsules. Phase transition temperatures and enthalpies, morphology, and particle size distributions of the microcapsules were analyzed using differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and particle size analyzer instruments, respectively. FT-IR spectroscopy was used to prove the presence of the thermochromic system in the microcapsules. UV-Vis absorption bands of the thermochromic system (TS) and microencapsulated thermochromic system (MTS) at both below and above the melting temperature of the solvent were obtained by using a UV-Vis spectrophotometer. The visible color change depending on temperature was monitored for each microcapsule individually by using a digital camera. Spherical morphology and unimodal particle size distribution of the microcapsules were determined by means of SEM photographs and particle size distribution curve analysis. The mean particle sizes of the produced microcapsules varied in a range of 16.0-35.2 μm. The digital camera photographs and the UV-Vis absorbance curves proved that color changed between dark blue and light blue depending upon the temperature change. Meanwhile, the produced microcapsules were proven for an excellent heat storage capacity for thermal energy storage owing to phase changing of the tetradecanol solvent used in the thermochromic system. The melting enthalpy of the microcapsules ranged from 145.5 J/g to 193.4 J/g.
KeywordsMicrocapsules Thermochromic system Leuco dye PMMA Thermal properties
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