Layer structure of quaternary-ammonium-salt-type amphiphilic gemini and trimeric ionic liquids

The layered structures formed by quaternary-ammonium-salt-type amphiphilic ionic liquids, including monomeric, identical and nonidentical alkyl chain-containing gemini, and star- and linear-structured three alkyl chain-containing trimeric types, were investigated by wide-angle X-ray scattering. A polyoxyethylene-type nonionic surfactant (C12EO6) was added to these amphiphilic ionic liquids, and the resulting layered structures were also elucidated. The spacing of the layers of the amphiphilic gemini ionic liquids increased with increasing fixed alkyl chain length in the two alkyl chains and differed according to the degree of alkyl chain dissymmetry. Amphiphilic trimeric ionic liquids displayed smaller layer spacings in linear structures than star structures, suggesting that the alkyl chains in the latter are loosely packed in layers due to the flexible spacer radiating from a central tertiary amine. Conversely, the alkyl chains in the linear structures are orderly and densely packed due to their close proximity. The addition of C12EO6 to the amphiphilic gemini and trimeric ionic liquids led to more ordered layers formed by the hydrophobic moiety, whereby the order decreased with increasing C12EO6 concentration. (C) 2021 Elsevier B.V. All rights reserved.