Lyotropic liquid crystal phases of monoolein in protic ionic liquids

The Journal of Chemical Physics

Monoolein-based liquid crystal phases are established media that are researched for various biological applications, including drug delivery. While water is the most common solvent for self-assembly, some ionic liquids (ILs) can support lipidic self-assembly. However, currently, there is limited knowledge of IL-lipid phase behavior in ILs. In this study, the lyotropic liquid crystal phase behavior of monoolein was investigated in six protic ILs known to support amphiphile self-assembly, namely ethylammonium nitrate, ethanolammonium nitrate, ethylammonium formate, ethanolammonium formate, ethylammonium acetate, and ethanolammonium acetate. These ILs were selected to identify specific ion effects on monoolein self-assembly, specifically increasing the alkyl chain length of the cation or anion, the presence of a hydroxyl group in the cation, and varying the anion. The lyotropic liquid crystal phases with 20–80 wt. % of monoolein were characterized over a temperature range from 25 to 65 °C using synchrotron small angle x-ray scattering and cross-polarized optical microscopy. These results were used to construct partial phase diagrams of monoolein in each of the six protic ILs, with inverse hexagonal, bicontinuous cubic, and lamellar phases observed. Protic ILs containing the ethylammonium cation led to monoolein forming lamellar and bicontinuous cubic phases, while those containing the ethanolammonium cation formed inverse hexagonal and bicontinuous cubic phases. Protic ILs containing formate and acetate anions favored bicontinuous cubic phases across a broader range of protic IL concentrations than those containing the nitrate anion.

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Lyotropic liquid crystal phases of monoolein in protic ionic liquids

Stefan Paporakis a, Stuart J. Brown a, Connie Darmanin b, Susanne Seibt c, Patrick Adams a, Michael Hassett a, Andrew V. Martin a, Tamar L. Greaves a

a. School of Science, College of STEM, RMIT University, 124 La Trobe Street, Melbourne VIC 3000, Australia

b. La Trobe Institute for Molecular Science, Department of Mathematical and Physical Sciences, School of Computing Engineering and Mathematical Science, La Trobe University, Bundoora VIC 3086, Australia

c. SAXS/WAXS Beamline, Australian Synchrotron, ANSTO, 800 Blackburn Road, VIC-3168 Clayton, Australia

DOI: https://doi.org/10.1063/5.0180420

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