Characterization of thermal performance of a solid–solid phase change material, di-n-hexylammonium bromide, for potential integration in building materials

Di-n-hexylammonium bromide ((n-C6H13)2NH2Br) undergoes a solid–solid phase transition at about 20 °C. The fact that it remains as a solid phase, yet the transition has a rather large enthalpy change (85 J g−1) suggests possible advantages as a phase change material (PCM) for integration into building materials. We investigated the phase change of (n-C6H13)2NH2Br in its pure form, and as a 30 mass% composite in gypsum. In the latter, we show that after 1000 cycles, which would correspond to about 3 years of use as a solar energy storage material, the temperature of the transition changes by less than 1 K and the enthalpy of transition is reduced by less than 3%. We also report the heat capacity and thermal conductivity of (n-C6H13)2NH2Br in the temperature range below and above the phase transition, and the volume change associated with the transition.