Surface Tension and Viscosity of Binary Mixtures of the Fluorinated and Non-fluorinated Ionic Liquids [PFBMIm][PF6] and [C4C1Im][PF6] by the Pendant Drop Method and Surface Light Scattering

• Published in: International journal of thermophysics Vol. 41; no. 10
• Main Authors: Koller, Thomas M., Lenahan, Frances D., Schmidt, Patrick S., Klein, Tobias, Mehler, Julian, Maier, Florian, Rausch, Michael H., Wasserscheid, Peter, Steinrück, Hans-Peter, Fröba, Andreas P.
• Format: Journal Article
• Language: English
• Published: New York Springer US 2020; Springer Nature B.V
• Subjects: Binary mixtures; Classical Mechanics; Condensed Matter Physics; Fluorination; Geophysics; Industrial Chemistry/Chemical Engineering; Ionic liquids; Light scattering; Photoelectrons; Physical Chemistry; Physics; Physics and Astronomy; Properties (attributes); Solvents; Surface properties; Surface tension; Thermodynamics; Thermophysical properties; Viscosity; Viscosity; Ionic liquids; Pendant drop method; Surface tension; Mixtures; Surface light scattering
• ISSN: 0195-928X; 1572-9567
• DOI: 10.1007/s10765-020-02720-w

Mixtures of fluorinated and non-fluorinated ionic liquids (ILs) show a distinct structural organization in the bulk and at the surface. To understand how such microscopic effects influence the macroscopic bulk and surface properties of IL mixtures, knowledge of corresponding thermophysical properties including viscosity and surface tension is required yet lacking. With the intention of investigating surface enrichment effects of the fluorinated IL [PFBMIm][PF 6 ] (3-methyl-1-(3,3,4,4,4-pentafluorobutyl)imidazolium hexafluorophosphate) in mixtures with the structurally similar, non-fluorinated IL [C 4 C 1 Im][PF 6 ] (1-butyl-3-methylimidazolium hexafluorophosphate) observed with angle-resolved X-ray photoelectron spectroscopy (ARXPS), the pendant drop method and surface light scattering (SLS) were applied in the present study to determine surface tension and dynamic viscosity between (293 and 368) K. By adding small amounts of [PFBMIm][PF 6 ] up to 9 mol %, a distinct increase in the viscosity and decrease in the surface tension of the mixtures relative to the properties of pure [C 4 C 1 Im][PF 6 ] was found. This behavior reflects the nanosegregated structure in the bulk and at the surface of the binary IL mixtures. Using the results about the pronounced surface enrichment of the fluorinated chain of [PFBMIm][PF 6 ] quantified by ARXPS, a linear mixing rule for the surface tension of the IL mixtures based on the surface tensions of the pure ILs and the surface concentration of their most surface-active groups is suggested.