The wormlike micelles formed using an ionic liquid surfactant and polar organic solvents at low temperature without additives and their lubricant properties

Wormlike Micellar Glycerol Solutions Formed from a Double-Tailed Surfactant with Two Quaternary Ammonium Head Groups

Herein, a quaternary ammonium surfactant with dual heads and tails, N1,N1,N1,N3,N3-pentamethyl-N3-(3-(2-tetradecylhexadecanamido)propyl)propane-1,3-diaminium dibromide, abbreviated as Di-C14-N2, was synthesized. For the first time, clear observation of aggregate structures formed by surfactants in pure glycerol systems was achieved using cryogenic transmission electron microscopy (cryo-TEM). The system's rheological properties were analyzed using both steady-state shear and oscillatory rheological measurements. The lubricating efficiency of the Di-C14-N2 glycerol solution was assessed for its tribological properties using a tribological wear tester, white light interferometer, and scanning electron microscope. In glycerol, Di-C14-N2 formed long wormlike micelles, which resulted in a glycerol solution with the zero-shear viscosity of 1013 Pa·s at 90 mM, which is the most viscous glycerol system up to now. The system displayed distinct rheological properties from the aqueous system, as evidenced by two intersections in the loss and storage moduli. The formed wormlike micelles in glycerol lead to a significant alteration in the viscoelasticity of the system, thus endowing the Di-C14-N2 glycerol solution with potential as an eco-friendly lubricant. The friction coefficient of the system was found to be 23% lower and the wear rate was 83% lower than that of pure glycerol after the addition of Di-C14-N2. This demonstrates that the addition of Di-C14-N2 greatly improves the frictional properties of pure glycerol. This study offers the possibility of directly observing the aggregate structures formed by surfactants in pure glycerol systems. It contributes to the exploration of the self-assembly behavior of surfactants in nonaqueous polar media, thereby aiding in a deeper understanding of the correlation between molecular structure, mesoscale structure, and macroscopic properties.

Significantly Affected Lubrication Behavior of Silicone Oil Lubricated Si3N4/Glass Contact after Cleaning with Different Solvents

Conventional methyl silicone oils have poor lubricating properties in boundary lubrication regions, particularly for ceramic/oxide point contact lubrication. In this study, the residues of various organic solvents on the surfaces of Si₃N₄ spheres/glass disks were used to determine their effect on the lubricating properties of silicone oil 200. The minute ethanol residues significantly enhanced the antifriction and antiwear properties of silicone oil. Compared to the blank sample, the coefficient of friction (COF) and wear volume of silicone oil 200 with the residual ethanol friction pair were reduced by >40% and >98%, respectively. Being immiscible with silicone oil, the minute ethanol residues also removed impurities from the glass surface and maintained a clean interface, thus effectively blocking direct interactions between the friction pair interfaces. In addition, the residual ethanol reduced the atomic force microscope probe-to-glass surface adhesive force in the silicone oil 200 environment, thus allowing it to maintain low COF and wear rates over a broader range of speeds, loads, and times. In contrast to previous work, this study is the first to effectively regulate the lubrication properties of silicone oil using a residual organic solvent. The findings further verified that the adsorption of vapor molecules can significantly alter the surface forces between interfaces. Thus, adjusting the adhesion force through trace amounts of organic solvent residues may provide novel research inputs, thereby guiding the expansion and scope of silicone oil lubrication applications.

In situ formation and dispersion of lanthanide complexes in wormlike micelles

Lanthanide-containing, water-based fluids normally suffer from low photoluminescent (PL) and/or colloidal stability, which greatly hinders their applications. Herein, we report the preparation of PL fluids which contain in situ formed europium complexes in aqueous solution. The strategy first relies on the construction of wormlike micelles by mixing a zwitterionic surfactant (tetradecyldimethylaminoxide, C₁₄DMAO) and a tridentate ligand for a lanthanide cation (2,6-dipicolinic acid, DPA) in water. The addition of the dual-functionalized DPA to an aqueous solution of C₁₄DMAO (100 mol L^-1) induced non-monotonic rheological changes, with the expected formation of a pseudogemini surfactant at a DPA-to-C₁₄DMAO molar ratio of approximately 1 : 2. When a third component of EuCl₃ is introduced to this system, complexes formed in situ between Eu³⁺ and DPA, resulting in bright red-emission. Besides DPA, C₁₄DMAO is also involved in the complexation, which squeezes out water molecules and greatly improves the PL stability of the fluid. The synergetic effect among Eu³⁺, DPA and C₁₄DMAO leads to the high colloidal stability of the fluid, opening the door for a wide range of potential applications. Further tests indicate that this strategy can be easily expanded to other lanthanide cations such as Tb³⁺.