Mesostructure and physical properties of aqueous mixtures of the ionic liquid 1-ethyl-3-methyl imidazolium octyl sulfate doped with divalent sulfate salts in the liquid and the mesomorphic states
Artikel i vetenskaplig tidskrift, 2018

This paper extends the study of the induced temperature change in the mesostructure and in the physical properties occurring in aqueous mixtures of the ionic liquid 1-ethyl-3-methyl imidazolium octyl-sulfate [EMIm][OSO 4 ]. For some compositions, these mixtures undergo a phase transition between the liquid (isotropic in the mesoscale) and the mesomorphic state (lyotropic liquid crystalline) at about room temperature. The behavior of mixtures doped with a divalent metal sulfate was investigated in order to observe their applicability as electrolytes. Calcium sulfate salt is almost insoluble even in the 20 wt% water mixture. The magnesium salt, in contrast, can be dissolved up to concentrations of 730 ppm in the same mixture and it has a profound impact on its properties. Six aqueous mixtures (with water content from 10 wt% to 33 wt%) of [EMIm] [OSO 4 ] were saturated with magnesium sulfate salt, producing the ternary mixture [EMIm] [OSO 4 ] + H 2 O + MgSO 4 . Viscosity, density and ionic conductivity for these samples were measured from 10 °C to 90 °C. In addition, SAXS, FTIR, diffussion NMR and Raman spectroscopy of the most interesting samples have been performed, and structural data indicate a transition between a hexagonal lyotropic liquid crystalline phase below and an isotropic solution phase above room temperature. The octyl sulfate anions of the cylindrical micelles in the hexagonal phase are coordinated with water molecules through H-bonds (about four per sulfate anion), while the [EMIm] cations seem to be poorly coordinated and so free to move. Inorganic salt addition reinforces that network, increasing the phase transition temperature.


O. Cabeza

Universidade Da Coruna

L. Segade

Universidade Da Coruna

M. Dominguez-Perez

Universidade Da Coruna

E. Rilo

Universidade Da Coruna

David Ausín

Universidade Da Coruna

Anna Martinelli

Chalmers, Kemi och kemiteknik, Tillämpad kemi

Negin Yaghini

Chalmers, Kemi och kemiteknik, Tillämpad kemi, Teknisk ytkemi

Bernhard Gollas

Technische Universität Graz

Manfred Kriechbaum

Technische Universität Graz

Olga Russina

Sapienza, Università di Roma

Alessandro Triolo

Consiglio Nazionale delle Ricerche

E. Lopez-Logo

Universidade de Santiagode Compostela

Luis M. Varela

Universidade de Santiagode Compostela

Physical Chemistry Chemical Physics

1463-9076 (ISSN) 1463-9084 (eISSN)

Vol. 20 8724-8736


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