Phase behaviour and aggregate structures of the surface-active ionic liquid [BMIm][AOT] in water

Yunxiao Zhang; Joshua B Marlow; Kathleen Wood; Jianan Wang; Gregory G Warr; Hua Li; Rob Atkin

doi:10.1016/j.jcis.2023.08.049

Phase behaviour and aggregate structures of the surface-active ionic liquid [BMIm][AOT] in water

J Colloid Interface Sci. 2023 Dec 15;652(Pt A):749-757. doi: 10.1016/j.jcis.2023.08.049. Epub 2023 Aug 9.

Authors

Yunxiao Zhang¹, Joshua B Marlow², Kathleen Wood³, Jianan Wang¹, Gregory G Warr², Hua Li⁴, Rob Atkin⁵

Affiliations

¹ School of Molecular Sciences, The University of Western Australia, Perth, Western Australia, Australia.
² School of Chemistry and Sydney Nano Institute, The University of Sydney, NSW 2006, Australia.
³ Australian Nuclear Science and Technology Organisation, Lucas Heights, New South Wales 2234, Australia.
⁴ School of Molecular Sciences, The University of Western Australia, Perth, Western Australia, Australia; Centre for Microscopy, Characterisation and Analysis, The University of Western Australia, Perth, Western Australia, Australia. Electronic address: Hua.Li@uwa.edu.au.
⁵ School of Molecular Sciences, The University of Western Australia, Perth, Western Australia, Australia. Electronic address: Rob.Atkin@uwa.edu.au.

PMID: 37582670
DOI: 10.1016/j.jcis.2023.08.049

Abstract

Hypothesis: The surface-active ionic liquid, 1-butyl-3-methylimidazolium 1,4-bis-2-ethylhexylsulfosuccinate ([BMIm][AOT]), has a sponge-like bulk nanostructure consisting of percolating polar and apolar domains formed by the ion charge groups and alkyl chains, respectively. We hypothesise that added water will swell the polar domains and change the liquid nanostructure.

Experiments: Small angle X-ray scattering (SAXS), small angle neutron scattering (SANS) and polarizing optical microscopy (POM) were used to investigate the nanostructure of [BMIm][AOT] as a function of water content. Differential scanning calorimetry (DSC) was employed to probe the thermal transitions of [BMIm][AOT]-water mixtures and the mobility of water molecules.

Findings: SAXS, SANS and POM show that at lower water contents, [BMIm][AOT]-water mixtures have a sponge-like nanostructure similar to the pure SAIL, at medium water contents a lamellar phase forms, and at high water contents vesicles form. DSC results reveal that water molecules are supercooled in the lamellar phase. For the first time, results reveal a series of transitions from inverse sponge, to lamellar then to vesicles, for [BMIm][AOT] upon dilution with water.

Keywords: Lamellar; Phase sequence; Sponge-like; Surface-active ionic liquid; Vesicle.