Phosphonium cation-based ionic liquids as neat lubricants: Physicochemical and tribological performance

© 2015 Elsevier Ltd.This paper studies physicochemical properties (density, viscosity, corrosion, thermogravimetry, and conductivity) and tribological behavior of five phosphonium cation-based ionic liquids ([P66614][BEHP], [P66614][C8C8PO2], [P66614][NTf2], [P44414][DBS], and [P4442][DEP]) as neat lubricants within steel-steel contact. A reciprocating ball-on-disc configuration was used to perform tribological tests. Worn surfaces were analyzed by confocal microscopy, SEM, EDS and XPS. Main results showed that: [P66614][NTf2], [P44414][DBS], and [P4442][DEP] showed corrosion activity; the ionic liquids with more reactive phosphate type anion ([P66614][BEHP] and [P4442][DEP]) had the best tribological behavior; the best tribological results were related to the tribofilm formation of two phosphate species

Phase Behavior of 1-Dodecyl-3-methylimidazolium Fluorohydrogenate Salts (C 12

The effects of the HF composition, n, in 1-dodecyl-3-methylimidazolium fluorohydrogenate salts (C₁₂MIm(FH)ₙF, n = 1.0–2.3) on their physicochemical and structural properties have been investigated using infrared spectroscopy, thermal analysis, polarized optical microscopy, X-ray diffraction, and anisotropic ionic conductivity measurements. The phase diagram of C₁₂MIm(FH)ₙF (n vs transition temperature) suggests that C₁₂MIm(FH)ₙF is a mixed crystal system that has a boundary around n = 1.9. For all compositions, a liquid crystalline mesophase with a smectic A interdigitated bilayer structure is observed. The temperature range of the mesophase decreases with increasing n value (from 61.8 °C for C₁₂MIm(FH)₁.₀F to 37.0 °C for C₁₂MIm(FH)₂.₃F). The layer spacing of the smectic structure decreases with increasing n value or increasing temperature. Two structural types with different layer spacings are observed in the crystalline phase (type I, 1.0 ≤ n ≤ 1.9, and type II, 1.9 ≤ n ≤ 2.3). Ionic conductivities parallel and perpendicular to the smectic layers (σ|| and σ⊥) increase with increasing n value, whereas the anisotropy of the ionic conductivities (σ||/σ⊥) is independent of the n value, since the thickness of the insulating sheet formed by the dodecyl group remains nearly unchanged