In this work, novel binary deep eutectic solvents (DESs) have been synthesized using pyrogallol (PY) as a hydrogen bond donor (HBD) and quaternary ammonium salts, choline chloride (ChCl), n-dodecyltrimethylammonium bromide (n-DDTMAB), tetraethylammonium bromide (TEAB), tetrapropylammonium bromide (TPAB), and tetrabutylammonium bromide (TBAB), as hydrogen bond acceptors (HBAs) and their physical properties were measured at different temperatures. The effects of temperature, alkyl chain length of HBAs, and molar ratio on the physical properties of the DESs were studied. It was found that the values of density, speed of sound, conductivity, viscosity, refractive index, and surface tension of the DESs follow the order [TEAB:PY] > [TPAB:PY] > [TBAB:PY]. The effect of different molar ratios on the physical properties shows that the values of density, conductivity, viscosity, and refractive index of the DESs follow the order [ChCl:PY(1:2)] > [ChCl:PY(1:1)], and the speed of sound and surface tension values follow the reverse order. The results show that the strength of the interactions between the investigated HBAs and PY follows the order [TBAB:PY] > [TPAB:PY] > [TEAB:PY] > [n-DDTMAB:PY] and [ChCl:PY(1:2)] > [ChCl:PY(1:1)], and the packing effect follows the reverse order. The chemical structures, purities, and interactions of DESs between the HBAs and HBD were investigated using 1H and 13C nuclear magnetic resonance and Fourier transform infrared analyses. The measured physical properties of the new DES mixtures that have been studied in this work provide useful information about their application in different industrial fields.
