Thermal properties and structural characterizations of new types of phase change material: Anhydrous and hydrated palmitic acid/camphene solid dispersions

Two new types of phase change material anhydrous and hydrated palmitic acid/camphene solid dispersions (PA1CA1) are prepared and characterized by low-temperature differential scanning calorimetry, powder X-ray diffraction, small-angle X-ray scattering and temperature-history method. Their microstructures contain nanometer-sized palmitic acid (PA) crystallites with lamellar periodicity dispersed in a partially amorphous plastic crystalline camphene (CA) matrix. The PA phase apparently possesses a relatively high latent heat value inherited from the pristine crystalline PA of 229.7 ± 0.1 kJ kg^-1. The relatively high specific heat of solid, C_ps, for anhydrous PA1CA1 of 2.17 ± 0.06 kJ kg^-1 K^-1 is originated from the presence of disordered CA matrix. Hydration of PA1CA1 can further increase the C_ps to 2.61 ± 0.01 kJ kg^-1 K^-1. The mixing of partially amorphous CA, some PA and the small amount of water may have turned the matrix into more disorder due to their different bonding natures, molecular weights, and various molecular shapes and sizes.