Phase diagrams, eutectic mass ratios and thermal energy storage properties of multiple fatty acid eutectics as novel solid-liquid phase change materials for storage and retrieval of thermal energy

A series of binary and multiple fatty acid eutectics such as ternary eutectics, quaternary eutectics and quinary eutectics were successfully prepared and developed as solid-liquid phase change materials (PCMs) by using five kinds of individual fatty acids such as capric acid (CA), lauric acid (LA), myristic acid (MA), palmitic acid (PA), and stearic acid (SA) through melt blending followed by ultrasonication method. The eutectic phase diagrams of binary/multiple fatty acid eutectics were plotted and analyzed on the basis of Schrader equation and MATLAB software, and then their eutectic mass ratios were precisely determined by eutectic phase diagrams and differential scanning calorimetry (DSC) analyses. The deviations between the theoretical calculated eutectic mass ratios and the experimental determined eutectic mass ratios of some fatty acid eutectics could be attributed to the experimental errors of data obtaining from the DSC analyses, impurities of fatty acids and cumulative errors of calculation. The results of DSC indicated that phase change temperatures and enthalpies of the synthesized fatty acid eutectics gradually decreased with the increase of the number of components in the mixtures. The melting peak temperatures of the prepared binary eutectics, ternary eutectics, quaternary eutectics and quinary eutectics were varied from about 22 to 56 °C, from about 18 to 49 °C, from about 19 to 32 °C and about 17 °C, respectively. Their minimum and maximum melting enthalpies were about 127.2 kJ/kg and 204.7 kJ/kg, respectively. The spectra obtained from Fourier transformation infrared spectroscope showed that the binary/multiple fatty acid eutectics exhibited the similar carboxyl group with the single fatty acids and had stable chemical properties. The developed fatty acid eutectic mixtures were suitable for low temperature thermal energy storage applications such as solar water heating systems, building energy storage systems, and thermal regulating textiles.