Molar heat capacity of tetrabutylammonium chloride-based deep eutectic solvents and their binary water mixtures

The molar heat capacities of three tetrabutylammonium chloride (TBAC)-based deep eutectic solvents (DESs) and their binary water mixtures were investigated in this work. Results showed a linear dependence of the molar heat capacity with temperature for all water compositions as well the pure components. The molar heat capacity decreased with increasing water composition for all systems. The TBAC : triethylene glycol system (DES2) showed the highest molar heat capacity (445.00–479.67 J mol⁻¹ K⁻¹) followed by the TBAC : ethylene glycol system (DES3); (288.34–312.59 J mol⁻¹ K⁻¹), while the TBAC : glycerol system (DES1) had the lowest molar heat capacity (281.20–310.85 J mol⁻¹ K⁻¹) among the three DES systems. The excess molar heat capacity, C_P ^E, of the DES–water binary mixtures was determined. Results of C_P ^E showed positive C_P ^E for DES2 and negative C_P ^E for DES3 for the entire range of water composition. DES1 showed a mix of positive and negative C_P ^E values for the mixture. This behavior is explained as a result of the change in the intermolecular interaction between the DES–water molecules in the mixture compared with the DES–DES and water–water molecular interaction in the pure components.