The surface tension, density and refractive index of amino acid ionic liquids: [C3mim][Gly] and [C4mim][Gly]

The amino acid ionic liquids (AAILs) [C3mim][Gly] (1-propyl-3-methylimidazolium glycine) and [C4mim][Gly] (1-butyl-3-methylimidazolium glycine) have been prepared by the neutralization method and characterized by 1H NMR spectroscopy and differential scanning calorimetry (DSC). The values of their density, surface tension and refractive index were measured at different temperatures. Since the AAILs can form strong hydrogen bonds with water, small amounts of water are difficult to remove from the AAILs by common methods. In order to eliminate the effect of the impurity as water, the standard addition method (SAM) was applied to these measurements. The values of thermal expansion coefficients, α, surface excess energy, Ea, surface excess entropy, Sa, and molar refraction, Rm, for the AAILs were determined.

► Two amino acid ionic liquids (AAILs), [C3mim][Gly] and [C4mim][Gly] were prepared.
► The density, surface tension and refractive index for the AAILs were measured.
► The thermodynamic properties for the AAILs were determined.