Phase behavior and structural properties for the triton X-100/n-CnH2n+1COOH/H2O system

Microstructure and Tribological Properties of Lamellar Liquid Crystals Formed by Ionic Liquids as Cosurfactants

Lamellar liquid crystals (LLCs) have been shown to have lubrication properties in many documents due to their bilayer structure. Ionic liquids are often used as additive or surfactant in LLCs. However, ionic liquids used as cosurfactants, which lead to a transition from the hexagonal liquid crystals to LLCs, are relatively rare. Herein, the microstructure of Triton X-100/C _nmimNTf₂/H₂O LLCs formed by using 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquid (C _nmimNTf₂, n = 8, 12, 16) as cosurfactant has been determined by polarized light microscopy, small angle X-ray scattering, and ²H NMR technique, and their rheological and tribological properties were investigated. These LLCs show good friction-reducing and antiwear performances. The correlation between the microstructure of the LLCs and their lubricating mechanism is established. The increase of the concentration of C _nmimNTf₂ and the length of alkyl chain in the LLCs can lead to an obvious reduction in friction coefficients and wear volumes, which are attributed to the higher order of amphiphilic molecules, the thickness of the amphiphilic bilayer, and the smaller cross-sectional area of the polar head group at the hydrophilic and hydrophobic interfaces. The protective film formed by the physical adsorption of ionic liquid LLCs on the surface of friction disk pair and the tribochemical reaction has effectively promoted the lubrication effect. The good lubricating property and antiwear capability indicate their promising and potential applications in water lubrication and biological lubrication.

Improvement in lubricating properties of TritonX-100/n-C10H21OH/H2O lamellar liquid crystals with the amphiphilic ionic liquid 1-alkyl-3-methylimidazolium hexafluorophosphate

The applications of ionic liquids (ILs)/lamellar liquid crystals (LLCs) have great potential in nanotribology because they could be used where conventional oils could not work. To clarify the lubricating mechanism, herein, ILs/LLCs lubricants were prepared by addition of amphiphilic 1-alkyl-3-methylimidazolium hexafluorophosphate (C_nmimPF₆, n = 8, 12) into TritonX-100/n-C₁₀H₂₁OH/H₂O LLCs with different concentration. The influence of alkyl chain lengths of ILs on the microstructures and the tribological properties of LLCs were investigated. The phase structure parameters and the tribological properties of the LLCs in the presence of C_nmimPF₆ were analyzed via freeze-fracture transmission electron microscopy (FF-TEM), the small-angle X-ray scattering (SAXS) technique, oscillating reciprocating friction and wear tester. Compared with the LLCs without C_nmimPF₆, 4.5 wt% C_nmimPF₆ /LLCs can reduce the friction and wear of sliding pairs. The better lubricating property and antiwear capability of the C_nmimPF₆/LLCs may be attributed to the increasing of the interlayer thickness d and the decreasing of the bilayer thickness d₀ in microstructures. This work provides a better understanding of the relationship between the microstructures and friction wear performances of ILs/LLCs.