Effect of protic ionic liquid and surfactant structure on partitioning of polyoxyethylene non-ionic surfactants

Inga L. Topolnicki, Paul A. FitzGerald, Rob Atkin, Gregory G. Warr

Research output: Contribution to journalArticle

14 Citations (Scopus)

Abstract

The partitioning constants and Gibbs free energies of transfer of poly(oxyethylene) n-alkyl ethers between dodecane and the protic ionic liquids (ILs) ethylammonium nitrate (EAN) and propylammonium nitrate (PAN) are determined. EAN and PAN have a sponge-like nanostructure that consists of interpenetrating charged and apolar domains. This study reveals that the ILs solvate the hydrophobic and hydrophilic parts of the amphiphiles differently. The ethoxy groups are dissolved in the polar region of both ILs by means of hydrogen bonds. The environment is remarkably water-like and, as in water, the solubility of the ethoxy groups in EAN decreases on warming, which underscores the critical role of the IL hydrogen-bond network for solubility. In contrast, amphiphile alkyl chains are not preferentially solvated by the charged or uncharged regions of the ILs. Rather, they experience an average IL composition and, as a result, partitioning from dodecane into the IL increases as the cation alkyl chain is lengthened from ethyl to propyl, because the IL apolar volume fraction increases. Together, these results show that surfactant dissolution in ILs is related to structural compatibility between the head or tail group and the IL nanostructure. Thus, these partitioning studies reveal parameters for the effective molecular design of surfactants in ILs. Surfactants in ionic liquids: The dissolution and solvation of the hydrophilic and hydrophobic components of non-ionic surfactants in ionic liquids are affected by solvent nanostructure and hydrogen bonding. The polar domains of protic ionic liquids ethyl- and propylammonium nitrate are, thermodynamically speaking, remarkably water-like.

Original languageEnglish
Pages (from-to)2485-2489
Number of pages5
JournalChemPhysChem
Volume15
Issue number12
DOIs
Publication statusPublished - 25 Aug 2014
Externally publishedYes

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