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

Wormlike micelles (or reverse wormlike micelles) are flexible cylindrical chains that are normally formed in water (or a nonpolar organic solvent) at 25.0 degrees C or above; the formation of wormlike micelles at lower temperatures is rare. Here, we have reported wormlike micelles formed at low temperature using an ionic liquid surfactant (1-octadecyl-3-nonyl imidazolium bromide) in polar organic solvents (including 1,3-propanediol, 1,2-propylene glycol, N,N-dimethylformamide, and glycerol/1,2-propylene glycol mixture) in the absence of any additives. The viscoelasticity and morphology of the wormlike micelles were studied using rheology, small-angle X-ray scattering, and cryo-transmission electron microscopy. The viscoelastic properties of the wormlike micelles in polar solvents are affected by the solvent type (or the weight ratio of glycerol to 1,2-propylene glycol), surfactant concentration, and temperature. Moreover, the G ' and G '' crossover twice in the dynamic curves, which is different from the case in water. The first crossover (at low frequency) corresponds to the relaxation time for the alkyl chains to disentangle from the transient network, and the second crossover (at high frequency) is related to the segmental motion of the chains. Furthermore, the tribological performance of these wormlike micelles is investigated at low temperature. It is found that the protective film (formed by the physical adhesion of the wormlike micelles on the surface of friction disk pair) and the tribochemical reaction together lead to good antifriction and antiwear performance, which indicates the application prospects of these wormlike micelles in low-temperature lubrication.

Automated summary

Wormlike micelles can form at low temperatures using an ionic liquid surfactant in polar organic solvents, showing viscoelastic properties and morphology which can be studied through rheology and microscopy. Their performance in polar solvents is affected by various factors, with crossover behavior in dynamic curves different from that in water. Additionally, the protective film and tribochemical reactions of the wormlike micelles contribute to their good antifriction and antiwear performance at low temperatures.