title: Trends in Hydrophilicity/Lipophilicity of Phosphonium Ionic Liquids As Determined by Ion-Transfer Electrochemistry.
abstract: Ionic liquids (ILs) have become valuable new materials for a broad spectrum of applications including additives or components for new hydrophobic/hydrophilic polymer coatings. However, fundamental information surrounding IL molecular properties is still lacking. With this in mind, the microinterface between two immiscible electrolytic solutions (micro-ITIES), for example, water|1,2-dichloroethane, has been used to evaluate the hydrophobicity/lipophilicity of 10 alkylphosphonium ILs. By varying the architecture around the phosphonium core, chemical differences were induced, changing the lipophilicity/hydrophilicity of the cations. Ion transfer (IT) within the polarizable potential window (PPW) was measured to establish a structure-property relationship. The Gibbs free energy of IT and the solubility of their ILs were also calculated. For phosphonium cations bearing either three butyl or three hydroxypropyl groups with a tunable fourth arm, the latter displayed a wide variety of easily characterizable IT potentials. The tributylphosphonium ILs, however, were too hydrophobic to undergo IT within the PPW. Utilizing a micro-ITIES (25 μm diameter) housed at the tip of a capillary in a uniquely designed pipet holder, we were able to probe beyond the traditional potential window and observe ion transfer of these hydrophobic phosphonium ILs for the first time. A similar trend in lipophilicity was determined between the two subsets of ILs by means of derived solubility product constants. The above results serve as evidence of the validation of this technique for the evaluation of hydrophobic cations that appear beyond the conventional PPW and of the lipophilicity of their ILs.
authors.affiliation: Sorbonne Paris Cité, Paris Diderot University, Interfaces, Traitements, Organisation et Dynamique des Systèmes , CNRS-UMR 7086, 15 rue J.A. Baïf, 75013 Paris, France.|Center for Advanced Materials and Biomaterials Research (CAMBR), Department of Chemistry, The University of Western Ontario , Chemistry Building, 1151 Richmond Street, London, Ontario N6A 5B7, Canada.
authors.forename: T Jane
authors.initials: TJ
authors.lastname: Stockmann
authors.affiliation: Center for Advanced Materials and Biomaterials Research (CAMBR), Department of Chemistry, The University of Western Ontario , Chemistry Building, 1151 Richmond Street, London, Ontario N6A 5B7, Canada.|Max Planck Institute for Colloids and Interfaces , Am Mühlenberg 1, 14476 Potsdam, Germany.
authors.forename: Ryan
authors.initials: R
authors.lastname: Guterman
authors.affiliation: Center for Advanced Materials and Biomaterials Research (CAMBR), Department of Chemistry, The University of Western Ontario , Chemistry Building, 1151 Richmond Street, London, Ontario N6A 5B7, Canada.
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Ragogna
authors.affiliation: Center for Advanced Materials and Biomaterials Research (CAMBR), Department of Chemistry, The University of Western Ontario , Chemistry Building, 1151 Richmond Street, London, Ontario N6A 5B7, Canada.
authors.forename: Zhifeng
authors.initials: Z
authors.lastname: Ding