Micro/nano encapsulation of some paraffin eutectic mixtures with poly(methyl methacrylate) shell: Preparation, characterization and latent heat thermal energy storage properties

Graphical abstract: Four kinds of micro/nano capsules, PMMA/(C17-C24), PMMA/(C19-C18), PMMA/(C19-C24) and PMMA/(C20-C24), were synthesized successfully as novel encapsulated phase change materials (PCMs) for the different monomer/PEM ratios via emulsion polymerization. The FTIR spectroscopy analysis confirmed the polymerization reaction occurred around the PEMs to be used as core materials. The POM, SEM and PSD analysis results showed that the synthesized PMMA/PEM micro/nano capsules had spherical shape appearance and micro/nano sizes. DSC analysis measurements revealed that the prepared micro/nano capsules containing the highest PEM content had a melting temperature range of about 20–36 °C and latent heat capacities in the range of about 86–169 J/g. TGA findings demonstrated that the encapsulated PEMs had good thermal reliability and chemical stability even after subjecting them to 5000 melting/freezing cycles. Furthermore, the prepared micro/nano capsules had reasonable thermal conductivity values and fine melting–freezing reversibility. - Highlights: • PSD analysis results showed that the encapsulated PEMs had micro/nano sized-spheres. • The encapsulated PEMs melt in the temperature range of about 20–36 °C. • The encapsulated PEMs had latent heat capacities of in the range of about 86–169 J/g. • TGA results demonstrated that they had good thermal stability. • The encapsulated PEMs had good thermal conductivity and phase change reversibility. - Abstract: This work is aimed to prepare, characterize and determine the latent heat thermal energy storage properties of micro/nano encapsulated paraffin eutectic mixtures (PEMs) with polymethylmethacrylate (PMMA) shell. The eutectic combination ratios and optimum melting temperatures of C17-C24, C19-C18, C19-C24 and C20-C24 mixtures were find out prior to the encapsulation processes. Four kinds of micro/nano capsules, PMMA/(C17-C24), PMMA/(C19-C18), PMMA/(C19-C24) and PMMA/(C20-C24), were synthesized effectively as novel encapsulated phase change materials (PCMs) via emulsion polymerization. The Fourier transform infrared (FTIR) spectroscopy analysis confirmed the polymerization reaction to be occurred around the PEM used as core material. The polarized optical microscopy (POM), scanning electron microscopy (SEM) and particle size distribution (PSD) analysis showed that the fabricated PMMA/PEM micro/nano capsules had spherical shape-appearances with micro/nano sizes. The differential scanning calorimetry (DSC) measurements revealed that the micro/nano capsules containing the highest PEM content had melting temperature range of about 20–36 °C and latent heat storage capacities of about 86–169 J/g. Thermogravimetry analysis (TGA) results verified that the encapsulated PEMs had good thermal reliability and chemical stability after repeated melting/freezing cycles for 5000 times. Furthermore, the synthesized PMMA/PEM micro/nano capsules had conceivable thermal conductivity values and reversible phase change behaviors