Densities, viscosities, and refractive indices of ternary mixtures of ionic liquid 1-hexyl-3-methylimidazolium chloride ([HMIm]Cl) + Schiff base, N,N'-bis(2-pyridylmethylidene)-1,2-diiminoethane (BPIE), a mixture of cis- and trans-isomers, + N,N-dimethylacetamide (DMA) were measured at T = 298.15 K. From the obtained data, apparent molar volumes (V-phi), corresponding experimental slopes (S-v), standard partial molar volumes (V-phi(0)), transfer volumes (Delta V-r(phi)0), viscosity B-coefficients, solvation numbers (S-n), and molar refractions (R-D) were calculated and discussed on the basis of (solute + solvent), and (solute + cosolute) interactions. As stated by cosphere overlap model (Yan et al., 2009), the negative transfer volumes obtained here show the dominance of (polar + nonpolar) interactions between the polar group of BPIE and the nonpolar alkyl chain of [HMIm]Cl and (nonpolar + nonpolar) interactions between the nonpolar groups of BPIE and the alkyl chain of [HMIm]Cl. The values of solvation numbers (S-n) were obtained as S-n > 2.5 and decrease as the concentration of BPIE in the mixtures increases. The S-n > 2.5 means that the IL is solvated in the mixtures, but the decreasing the S-n values indicates that the solvation of the ions of the ionic liquid decreases at higher concentrations of the Schiff base. (C) 2014 Elsevier Ltd. All rights reserved.