Lyotropic liquid crystal phases of phytantriol in a protic ionic liquid with fluorous anion.

Abstract

The phase behaviour of phytantriol in the protic ionic liquid (PIL) 1-methylimidazolium pentadecafluorooctanoate (MImOF) and four different MImOF-water compositions was investigated by small- and wide-angle X-ray scattering (SAXS/WAXS), cross polarised optical microscopy (CPOM) and infrared spectroscopy (IR). MImOF is a distinct protic ionic liquid in that it contains a fluorocarbon anion and a hydrocarbon cation. This leads to MImOF having an unusual liquid nanostructure, such that it contains fluorocarbon, hydrocarbon and polar domains. No lyotropic liquid crystal phases were observed for phytantriol in neat MImOF. However, on addition of water, lamellar, cubic Ia3¯d and micellar phases were observed for specific MImOF-phytantriol-water compositions at room temperature, and up to 60 °C. The phase behaviour for phytantriol in the solvent mixture of 25 wt%-MImOF-75 wt%-water was the most similar to the phytantriol-water phase diagram. Only this MImOF-water composition supported the Ia3¯d cubic phase, which had a lattice parameter between 100-140 Å compared to 86-100 Å in deionised water, indicating significant swelling due to the MImOF. IR spectroscopy showed that a percentage of the water molecules were hydrogen bonded to the N-H of the MIm cation, and this water decreased the hydrogen bonding present between the cation and anion of the ionic liquid. This investigation furthers our understanding of the interaction of ionic liquids with solutes, and the important role that the different IL nanostructures can have on influencing these interactions.