Molar Heat Capacity of Selected Type III Deep Eutectic Solvents

In this work, the molar heat capacity of type III deep eutectic solvents (DESs) for three quaternary salts was investigated in the temperature range of 298.15–353.15 K. Several hydrogen bond donors were used with the three salts to prepare the DESs. Melting and/or glass transition points of the DESs were also measured and presented. The results showed that the molar heat capacity for all systems increased almost linearly with temperature. In addition, the results showed that molar heat capacity is directly proportional to the molar mass of the DES. The molar heat capacity for all DES systems studied in this work ranged from 219.3 to 605.9 J·mol^–1·K^–1. The tetrabutylammonium chloride (TBAC)–urea DES system showed the highest molar heat capacity range of 590.1–605.9 J·mol^–1·K^–1 while the choline chloride (ChCl)–phenol system had the lowest range of 219.3–236.8 J·mol^–1·K^–1. The TBAC–urea DES system had the highest melting point (300.29 K) compared to all other DES systems in this work. Melting and/or glass transition points for all studied systems ranged from 224.8 to 300.29 K. This indicated that these solvents could be used in the liquid phase at room temperature for future applications.