Surfactant Stabilized Copper Nanoparticles Synthesis, Characterization And Investigation of Their Tribological Behavior As Additive In Lubricating Oil

F.A. Bezza, E.M.N. Chirwa
University of Pretoria,
South Africa

Keywords: antifriction, antiwear , microbial surfactant, tribologocal property, nanoparticles, lubricant additives

Summary:

Wear and friction are some of the major reasons for energy loss and failure of machineries in engines, gears, etc., which are vital for the smooth operation of mechanical systems in various industries. Lubrication of surfaces with oils fortified with special additives reduces wear and friction. Furthermore, addition of nanoparticles (NPs) into lubricating oil significantly reduces the friction coefficient and increases the load-bearing capacity of the friction parts in mechanical systems. Major challenges for using metal NPs as lubricant additives are agglomeration, and precipitation in oils. Due to their high surface energy associated with their small size and Vander Waals attractive interactions NPs tend to aggregate. To protect nanoparticle aggregation chemical surfactants are usually added as dispersant or surface modifier. However, environmental concerns mostly driven by new regulations aimed at managing the environment have led to the pursuit to find alternative microbial surfactants. The purpose of this study is synthesis of copper nanoparticles using water in oil microemulusion method using biosurfactant stabilization, transmission electron microscopy (TEM) and Scanning Electron Microscopy (SEM) characterization of the synthesized CuNPs and investigation of their potential application in improving tribological behavior of lubricant oil API CF/SF. Addition of copper nanoparticle additives in oil at 1.5 wt. % demonstrated significant reduction in the friction and wear between the lubricated surfaces compared to the stand-alone and 0.5 wt. % CuNP additives. The average reduction of coefficient of friction following the addition of surfactant stabilized CuNPs at 1.5 wt. % was 41 % while only 16.7% reduction was observed at the same amount of bare copper nanoparticle additives. The wear reduction for surfactant stabilized CuNPs at 1.5 wt.% addition was ~35.5% compared to 7.4% at 1.5 wt.% of bare CuNP additives. It can be observed that there is a very high variation in friction and wear reduction between bare and biosurfactant stabilized CuNPs additives. Transmission Electron Microscope (TEM) analysis revealed uniformly dispersed and small CuNPs free from agglomeration with ~70 nm diameter predominantly in the biosurfactant stabilized CuNPs compared to highly agglomerated bare CuNPs synthesized in the absence of the biosurfactant. From the TEM analysis, it can be inferred that the uniform size distribution and colloidal stability of the surfactant stabilized CuNPs helped increase antifriction and wear resistance of the lubricant oil. Our study revealed that reduced agglomeration and enhanced dispersion stability of nanoparticles displayed remarkable tribological performance of oil, demonstrating the potential significance of stabilized CuNPs in designing high-performance nanolubricating oils for practical uses.