Vegetable oil-based ionic liquid microemulsion biolubricants: Effect of integrated surfactants

We report the design of ionic liquid-in-vegetable oil microemulsion biolubricants which were stabilized by integrated surfactants of 1-octyl-3-methylimidazolium chloride ([C(8)mim][Cl]) and Triton X-100. Castor oil and 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) were used as the non-polar and polar phase, respectively. The phase behavior of the pseudo-ternary system at various temperatures was investigated, and the results showed that the addition of [C(8)mim][Cl] could enhance the driving force of constructing microemulsions, and could further improve their phase formation capacities. Conductivity measurement, dynamic light scattering, UV-vis spectrophotometry, and Fourier transform infrared spectroscopy combined with H-1 NMR were used to probe the conformational structure and formation mechanism. A possible structure for the [bmim][BF4]-in-castor oil microemulsion stabilized by mixed surfactants was proposed. In addition, kinematic viscosity, friction, and wear were measured to evaluate the tribological performance of the vegetable oil-based ionic liquid microemulsion biolubricants. The designed systems exhibited enhanced lubricant properties, which indicate promising practical industrial applications. (C) 2014 Elsevier B.V. All rights reserved.