The effect of alkyl chain length of the imidazole ionic liquid surfactants on the improving lubricating properties of the hexagonal lyotropic liquid crystal composed of the [C16imCn]Br/hydrotalcite/H2O

The hydrotalcites were dispersed in the hexagonal lyotropic liquid crystals (LLCs) composed of 1-hexadecyl-3-alkyl imidazolium bromide ([C(16)imC(n)]Br, n = 1, 2 and 3) and H2O. The effects of the hydrotalcite concentration and the alkyl chain length of the [C(16)imC(n)]Br on the properties and the lubricant performance of the [C(16)imC(n)]Br/hydrotalcite hexagonal LLCs were studied by small angle X-ray diffraction measurements, rheology and tribology. Compared with the pure hexagonal LLCs, the incorporation of hydrotalcite into the [C(16)imC(n)]Br hexagonal LLCs can increase the interlayer distances and the viscoelasticity of the hybrid hexagonal LLCs gradually. However, the friction coefficient and wear volume decrease firstly and then increase with the increasing of hydrotalcite content. With the increase of the alkyl chain length of the [C(16)imC(n)]Br, the viscoelasticity, the interlayer distance and the water permeability of the mixed LLCs gradually increase which decreases the friction coefficient and wear volume at the moderate hydrotalcite content. The mechanism of the effective improvement of lubrication performance of the hybrid hexagonal LLCs is the tribofilm formed by the physical adsorption and tribochemical reaction of [C(16)imC(n)]Br/hydrotalcite LLCs on the steel surface. (C) 2022 Elsevier B.V. All rights reserved.

Automated summary

This study investigates the effects of hydrotalcite concentration and alkyl chain length of [C(16)imC(n)]Br on the properties and lubricant performance of [C(16)imC(n)]Br/hydrotalcite hexagonal LLCs. The incorporation of hydrotalcite into hexagonal LLCs increases interlayer distances and viscoelasticity gradually. However, the friction coefficient and wear volume decrease initially and then increase with the increase of hydrotalcite content. Longer alkyl chain length of [C(16)imC(n)]Br leads to increased viscoelasticity, interlayer distance, and water permeability, which reduces the friction coefficient and wear volume at moderate hydrotalcite content. The improvement in lubrication performance is attributed to the formation of a tribofilm through physical adsorption and tribochemical reaction of [C(16)imC(n)]Br/hydrotalcite LLCs on the steel surface.