The thermodynamics of the activation for viscous flow of aqueous [C6mim][Ala] (1-hexyl-3-methylimidazolium alanine salt)

Abstract The values of density and viscosity for aqueous solution of ionic liquid (IL) based on alanine [C 6 mim][Ala] with various molalities were measured at T  = (288.15–328.15) K with interval 5 K. The activation energy, E η , for viscous flow of the solution was calculated. In terms of Jones-Dole equation, the viscosity B-coefficients with large positive value and dB/d T  0 were obtained and these facts implied that the ionic liquid is water-structure-making. According to Feakins, the contribution of the solute per mole to the free energy of activation for viscous flow of the solution, Δ μ †0 , or was called as the standard molar activation free energy, was obtained at T  = (288.15–328.15) K. The relationship between Δ μ 2 † 0 and the temperature is linear, so that the standard molar activation entropy Δ S 2 † 0 and enthalpy, Δ H 2 † 0 , were obtained. Under the constant molality of solution, Δ H 2 † 0 is a temperature-independent constant. It implies the activation process of the solute for viscous flow of aqueous [C 6 mim][Ala] is an isocoulombic reaction. On the basis of Eyring’s theory, a semi-empirical method to estimate the viscosity of aqueous [C 6 mim][Ala] was put forward and the estimated viscosity values of aqueous [C 6 mim][Ala] are in good agreement with the corresponding experimental ones.