Stability, thermal conductivity and rheological properties of graphene and MWCNT in nanolubricant using additive surfactants

Abstract

This study presents the stability, thermal conductivity and rheological properties of Graphene (GR) and Multi-wall carbon nanotube (MWCNT) in SUNISO SL68 Oil with different surfactants. Cetrimonium bromide (CTAB), Sodium Dodecylbenzene Sulfonate (SDBS), and Sorbitan monooleate (SPAN-80) are used as a surfactant. Zeta potential measurement was used to identify the agglomeration tendency of the samples. Visual observation, aided by an LED backlight, was used to investigate the sedimentation tendency of the samples. Thermal conductivity was measured to determine conductivity improvements of a nanolubricant with additive surfactants. Lastly, a cone and plate were used to measure the viscosity of the samples at different shear rates and temperatures. Zeta potential results were matched with visual observation results and CTAB is shown to be a better surfactant for both GR and MWCNT. Thermal conductivity analysis shows no significant improvement within the different surfactants, however, between 2% and 7% improvement is recorded when comparing nanolubricant to pure oil. A non-Newtonian fluid behaviour, specifically, Shear-thinning flow behaviour is observed in MWCNT nanolubricant samples, unlike the pure oil that shows a Newtonian fluid behaviour.