Abnormal temperature dependence of the viscosity of ethylammonium nitrate-methanol ionic mixtures

The shear viscosities of ionic fluids composed of ethylammonium nitrate (EAN) and methanol (MeOH) have been investigated as a function of the shear rate, the composition of the mixtures ( quoted as x, the mole fraction of EAN), and the temperature ( T) in the range 293-328 K. At low content of EAN (0.2 less than or equal to x less than or equal to 0.4), the solutions exhibit a non-Newtonian and a non-Arrhenius behavior. The viscosities of these solutions increase with the temperature when T > 313 K, but they are independent of the temperature at x = 0.6 and decrease for x > 0.6. Excess viscosities and excess Gibbs energies for the viscosity give evidence of the formation of strong hydrogen bonded complexes in solution for x < 0.6 and T > 318 K. For these systems, any increase in temperature favors the formation of hydrogen bonds between EAN and MeOH.