Improving thermal characteristics and stability of phase change material containing TiO2 nanoparticles after thermal cycles for energy storage

In this study, thermal characteristics and stability of TiO2/paraffin composites with and without sodium stearoyl lactylate (SSL) as a surfactant were evaluated. The TiO2/paraffin composites with 0.5, 0.7, 1, 2, 3, 4 wt% were prepared in two series, with and without the SSL. FE-SEM micrographs illustrated that adding the surfactant to the paraffin matrix could improve the dispersion of the nanoparticles efficiently. DSC analysis showed that the maximum latent heat of 165.1 and 167 J/g for nanocomposites occurs in 1 and 3 wt% for samples of TiO2/paraffin without and with the SSL, respectively. The thermal conductivity coefficient was enhanced with adding nanoparticles, considerably. An increase of 47.85% in the thermal conductivity was found for the paraffin containing 3 wt% of nanoparticles with the surfactant. TiO2/paraffin composite with 3 wt% was chosen as an optimal sample to consider the physical and thermal stability after several thermal cycles. TGA thermograms showed that thermal stability of the TiO2/paraffin/SSL composite (3 wt%), as compared to pure paraffin and TiO2/paraffin (3 wt%), was improved. It was found that the melting temperature and the latent heat of nanocomposites had inappreciable changes after several thermal cycles. The thermal conductivity of the nanocomposites approached the initial thermal conductivity of the pure paraffin, after several thermal cycles, while a marked decrease in thermal conductivity of pure paraffin was apparent.