Preparation and thermal properties of a novel pseudo ionic liquid phase change material for solar water heating system

At present, the thermal properties (melting point, thermal conductivity, etc.) of common phase change materials (PCMs) cannot be accurately modulated, which limits their application in larger fields. Pseudo ionic liquid phase change materials (PILPCMs) have presented great potential due to its tunable thermal property and high physicochemical stability. In this work, a novel PILPCM consisting of cetyltrimethylammonium bromide (CTAB) and urea is developed for the solar water heating system (SWHS) for hot water supply. First, the mass ration of CTAB to urea was optimized toward suitable PILPCM with desirable phase change behaviors. The eutectic formation mechanism of PILPCM was then interpreted by experimental ¹³CNMR and theoretical σ-profile characteristics. Afterward, the shape stability, thermal conductivity, supercooling degree, thermal stability and reliability were investigated systematically. The results showed that the formation of eutectic PILPCM was ascribed to the physical hydrogen-bonds between CTAB and urea. The CTAB-urea mixture in the mass ratio of 6:1 exhibited favorable melting point of 86.9 °C, the highest latent of 174.9 kJ/kg, excellent shape stability, low degree supercooling of about 3 °C as well as comparable thermal conductivity. Moreover, such PILPCM had satisfactory thermal stability and reliability, which was confirmed by notably higher temperature of thermal decomposition over the operating condition and slight changes of phase change behaviors after 100 thermal cycles. Conclusively, the fabricated PILPCM integrates the advantages of CTAB and urea, and shows considerable potential in the concerned SWHS case.