Vol. 3, Issue 7, Part R (2017)

Abstract
The densities, ρ, and viscosites, η, of mixtures of propanoic acid with equimolar mixtures of N,N-dimethyl formamide + methanol/ethanol/1-propanol, over the entire composition range of propanoic acid and including the pure liquids, have been measured at the temperatures T/K = 303.15, 313.15, and 323.15. From this experimental data, the excess molar volume, VEmVmE, deviation in viscosity, Δη, and excess Gibbs energy of activation of viscous flow, ΔG *E, have been determined at all three temperatures. The influence of temperature on these mixtures has been studied in terms of molecular interactions. The calculated deviation and excess parameters have been fitted to a Redlich–Kister type polynomial and the corresponding standard deviations were also evaluated. Negative values of VEmVmE and positive values of Δη and ΔG *E are observed at all temperatures over the entire composition range in the mixtures studied. The observed negative and positive values of various excess and deviation parameters are attributed to the existence of strong interactions, like dipole–dipole interactions, H-bonding between the carbonyl group of acid molecules and hydroxyl group of alcohol groups, geometrical fitting of smaller molecules into the voids created by larger molecules in the liquid mixtures. The strength of these interactions in the mixtures was found to decrease with the rise in temperature and increase with an increase of chain length of the alcohols. The derived partial molar volumes and excess partial molar volumes also support the VEmVmE results.