Differential scanning calorimetric study of nonionic surfactant mixtures with a room temperature ionic liquid, bmimBF4

The melting behavior of polyethyleneglycol dodecyl ethers (C12E6, C12E7, and C12E8) in a room temperature ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF4), was investigated by means of differential scanning calorimetry (DSC). The melting temperature as a function of the surfactant concentration, combined with the cmc curve and cloud point curve, provided phase diagrams for the surfactant/bmimBF4 mixtures in solvent-rich region. The characteristic feature of the mixtures is an existence of the Krafft temperature which is usually not observed with aqueous solutions of nonionic surfactants. The heat of fusion as a function of the surfactant concentration provided the interaction energy between the surfactant and bmimBF4. The interaction energy shows a linear dependence on the length of polyoxyethylene (POE) chain of the surfactants, which suggests that the solvation takes place around the POE chain.

Graphical abstractA Krafft point phenomenon is observed in solutions of nonionic surfactants in a room temperature ionic liquid, bmimBF4, contrary to the case of normal aqueous solutions.Figure optionsDownload full-size imageDownload high-quality image (103 K)Download as PowerPoint slide