Densities of aqueous mixtures of (choline chloride + ethylene glycol) and (choline chloride + malonic acid) deep eutectic solvents in temperature range 283.15–363.15 K

• For (DES + water) mixture, density decreases with increasing T within 283.15–363.15 K with quadratic dependence on T.
• Excess molar volume of aqueous mixtures of DES is significant and negative at all T and compositions.
• Density dependence on DES mole fraction follows exponential-rise-to-maxima.
• The density data imply presence of strong interactions between water and DES.
• Interstitial accommodation of water within H-bonded DES network is also strongly suggested.

Deep eutectic solvents (DESs) are emerging as a new class of biodegradable green solvents; a cost-effective alternative to the conventional room temperature ionic liquids and organic solvents. Hydrophilic nature of DES finds its applications in many industrial and chemical processes. Aqueous mixtures of DESs have potential to afford modified properties for specific applications. A comparative study of densities of two well-known DESs named as ethaline (mixture of choline chloride and ethylene glycol in 1:2 molar ratio) and maline (mixture of choline chloride and malonic acid in 1:2 molar ratio) and their aqueous mixtures in the temperature range 283.15–363.15 K is presented. Decrease in density with increasing temperature is found to follow a quadratic expression. Excess molar volumes of the aqueous mixtures of both ethaline and maline are found to be negative and significant at all temperatures and compositions. Absolute excess molar volume is found to decrease as the temperature is increased from 283.15 K to 323.15 K. For temperature above 323.15 K, the excess molar volume does not change much with further increase in temperature till 363.15 K. The outcomes hint at the presence of relatively stronger interactions, preferably H-bonding type, between water and ethaline/maline, as compared to those among water and among ethaline/maline molecules, respectively. The excess molar volumes at higher temperatures strongly indicate facile interstitial accommodation of water within H-bonded ethaline/maline network to be also present within these aqueous DES mixtures.