Thermodynamic investigation of a solid-solid phase change material: 2-Amino-2-methyl-1,3-propanediol by calorimetric methods

An important solid-solid phase change heat storage material (PCM) 2-amino-2-methyl-1,3-propanediol was investigated by calorimetric methods. The molar heat capacities of the compound were measured in the temperature range from 78 to 405 K by means of a small sample automated adiabatic calorimeter. A solid-solid and solid-liquid phase transitions were found at T = 351.598 K and 380.633 K, respectively, from the experimental Cp-T curve. The molar enthalpies and entropies of these transitions were determined to be 24.33 ± 0.02 kJ mol-1, 69.20 ± 0.07 J K-1 mol-1 for the solid-solid phase transition and 4.01 ± 0.01 kJ mol-1, 10.52 ± 0.01 J K-1 mol-1 for the solid-liquid phase transition, respectively. The thermodynamic functions (HT - H298.15) and (ST - S298.15), were derived from the heat capacity data in the temperature range of 78-405 K with an interval of 5 K. A precise oxygen-bomb combustion calorimeter was used to obtain the standard molar enthalpy of combustion and the standard molar enthalpy of formation, ΔcHm0 (C5H11NO2, cr) = (-3326.25 ± 0.52) kJ mol-1 and ΔfHm0 (C5H11NO2, cr) = (-213.37 ± 0.86) kJ mol-1. DSC and TG tests were performed to investigate the solid-solid and solid-liquid phase transition behaviors and its thermostability. The results were in agreement with those obtained from heat capacity measurements, which indicated that 2-amino-2-methyl-1,3-propanediol possesses typical solid-solid phase change material characteristics, such as, suitable transition temperature, high transition enthalpy and good thermal stability.