Evidence of change in the molecular organization of 1-n-butyl-3-methylimidazolium tetrafluoroborate ionic liquid solutions with the addition of water

Physico-chemical properties of ionic liquids like density, viscosity, conductivity, surface tension and excess molar volume are strongly dependent on their concentration in aqueous solutions. 1-n-Butyl-3-methylimidazolium tetrafluoroborate/water solutions, at 25 °C, shows two clearly distinguished behaviors, corresponding to a water-rich and a salt-rich region, with distinct physico-chemical properties. It is shown that [BMIm][BF4] exhibits surfactant properties. The results obtained are discussed in terms of the interactions between cations and anions of the ionic liquid and the water molecule. IR studies show that the addition of water modifies the organization of the ionic liquid molecules. The data collection reported is helpful for a variety of different technological applications and in particular for electrochemical applications, as capacitors, batteries and fuel cells among others.

Specific conductivity of the IL solutions increases in the water-rich region and decreases in the salt-rich region, exhibiting a maximum at IL mole fraction ca. 0.9. Increasing specific conductivity has been attributed to the weakness of the intermolecular interaction of the [BMIm][BF4] structure provoked by adding water, increasing the dissociation and, consequently, increasing the ionic mobility of the ionic species. The decrease in the intermolecular interaction between the anionic and cationic species of [BMIm][BF4] due to the addition of water has been shown by IR.Figure optionsDownload as PowerPoint slide