A new strategy for simultaneous photoluminescence and thermal energy storage/release: Microencapsulated phase change materials via nano-Y2O3 modified PW@CaCO3

Abstract

A multifunctional microencapsulated phase change material (PW@CaCO3/Y2O3) with both photoluminescence and thermal energy storage/release properties has been prepared by in situ polymerization. The material is based on the phase change material paraffin wax (PW) as its core, and the highly thermally conductive inorganic material CaCO3 is selected as the shell material to which a nano-Y2O3 material is attached. Five samples with different amounts of nano-Y2O3 incorporated in the shell are prepared. The microscopic morphology, chemical composition, crystal structure, thermal energy storage properties, thermal conductivity, thermal stability, as well as fluorescence spectra and intensities of the samples are experimentally measured and compared. The luminescence properties of nano-Y2O3 and the light enhancement phenomenon of microencapsulated phase change materials are also analyzed. The thermal properties are investigated, and it is found that the PC-Y3 sample (i.e., the mass ratio of PW:CaCO3:nano-Y2O3 is 100:100:3.0) exhibits the best thermal performance among the five samples with a melting enthalpy of (87.5 ± 2.5)  J/g, an encapsulation efficiency of (61.9 ± 1.2)%, a thermal energy storage efficiency of (62.1 ± 1.5)%, an average specific heat capacity of (1.38 ± 0.21) kJ/(kg K) in solid phase (10–20 °C) and (1.46 ± 0.02) kJ/(kg K) in liquid phase (70–80 °C), and a thermal conductivity of (1.55 ± 0.01) W/(m K) in solid phase that is six times that of the solid PW. A study of the optical properties revealed that the microcapsules emitted blue light at an excitation wavelength of 290.0 ± 2.2 nm. The fluorescence intensity appeared to be enhanced with the addition of nano-Y2O3. This microencapsulated phase change material has potential applications in areas where synchronization of fluorescence and thermal modulation is required; for example, some specific fluorescent sensors that are very sensitive to heat should operate at a fixed low temperature.