The apparent molar volume (ϕV) and viscosity B-coefficient have been estimated of 0.01 m, 0.03 m and 0.05 m aqueous nicotinic acid solutions in presence of the ionic liquids (IL), 1-butyl-2, 3 – dimethylimidazolium tetrafluoroborate (BdmimBF4) and 1-ethyl-3-methylimidazolium tosylate (EmimOTs) at 298 K, 303 K and 308 K from densities (ρ) and viscosities (η) measurements. The limiting apparent molar volumes (ϕV0) and experimental slopes (SV*) obtained from the Masson equation have been explained in terms of solute–solvent and solute–solute interactions respectively. The limiting apparent molar volumes of transfer (∆ϕV0) have been used to interpret various hydrophobic–hydrophilic and hydrophobic–hydrophobic group interactions between the solute and co-solute in aqueous medium. The viscosity data were examined using the Jones–Dole equation and the resulting parameter B has also been interpreted in terms of solute–solvent interactions in the solutions. Molar free energy of activation of viscous flow of the solvent, ∆µ10 and solute, ∆µ2° has been deduced to understand the stability of ground state over transition state.
