https://doi.org/10.1140/epjb/s10051-026-01175-6
Research - Condensed Matter
Formation of ionic liquid-in-water microemulsions using non-ionic surfactants: a comprehensive spectroscopic, microscopic, and rheological investigation
1
Department of Chemistry, Jamia Millia Islamia (Central University), New Delhi, India
2
Department of Chemistry, University of Allahabad (Central University), 211002, Prayagraj, U.P., India
3
Soft Matter Research Lab, Department of Chemistry, University of Kahmir, 190006, Srinagar, Jammu and Kashmir, India
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Received:
4
March
2026
Accepted:
22
April
2026
Published online:
22
May
2026
Abstract
Ionic liquid-based microemulsions are currently gaining more attention from research communities across the world owing to their immense application potential in various fields of science and technology. In this manuscript, we have studied the formation of ionic liquids-in-water (IL/W) microemulsions using hydrophobic ionic liquid (IL) 1-butyl-3-methylimidazolium hexafluorophosphate, BmimPF6 and nonionic surfactants: Tween-20, TX-100 and Brij-30. The solubility of hydrophobic BmimPF6 within each of these aqueous micellar solutions was found to increase with an increase in surfactant concentration. The formation of IL/W microemulsions by each of these non-ionic surfactants was characterised using UV–visible and fluorescence spectroscopy with fluorescein as the probe to monitor changes in the microenvironmental polarity. Fluorescence spectroscopy provided complementary insights into the solubilisation and distribution of the IL within the micellar structures. Electrical conductivity measurements further elucidated the ionic properties of the solutions, highlighting the influence of surfactant structure and IL concentration on the behaviour of microemulsions. The size distribution of the microemulsion droplets was determined using dynamic light scattering (DLS), and the stability and surface charge of the microemulsions were examined using zeta potential measurements. This study demonstrates the impact of non-ionic surfactants (Brij-30, TX-100 and Tween-20) on the formation of IL/W microemulsions. Furthermore, with greater IL concentrations, rheology investigations show the formation of a more reorganised microemulsion phase. Particularly in tween-20 systems, IL-induced changes to droplet size and interfacial organisation were confirmed by optical and confocal imaging. These findings demonstrate the significance of surfactant–IL interactions in regulating the stability and shape of microemulsions. The non-ionic surfactants and IL were shown to be stable and reactive by quantum chemical calculations. The results will further improve the future uses of these IL-based hybrid nano media in chemical, pharmacological and biotechnological processes, where they are preferable to combine surfactant systems with hydrophobic ionic liquid.
Supplementary Information The online version contains supplementary material available at https://doi.org/10.1140/epjb/s10051-026-01175-6.
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© The Author(s), under exclusive licence to EDP Sciences, SIF and Springer-Verlag GmbH Germany, part of Springer Nature 2026
Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.
