Ultrasound assisted shape regulation of CuO nanorods in ionic liquids and their use as energy efficient lubricant additives

Copper oxide nanorods (CuONR1) having a diameter of about 20–30 nm and a length of about 30–70 nm were prepared by simple chemical processing of copper salt. CuONR1 were morphologically reshaped, by sonication with 1-hexyl-3-methylimidazolium acetate and tetrabutylammonium acetate ionic liquids, to CuONR2 and CuONR3, respectively. Both CuONR2 and CuONR3, with a diameter of about 8–18 nm and a length of about 60–200 nm, exhibit high aspect ratios (length-to-breadth) compared to CuONR1. The XRD pattern reveals the monoclinic crystalline structure of CuONR1, which remains unchanged during their ultrasound treatment with ionic liquids. Dispersion stability and aspect ratio of CuO nanorods are found to play an important role in monitoring the lubrication characteristics. The results show that CuONR2 and CuONR3, stabilized by ionic liquids, exhibit excellent friction-reduction (15–43%) and improved anti-wear properties (26–43%) compared to the PEG 200 and 10W-40 engine oil. Lubricity enhancement is attributed to the synergistic effect of uninterrupted supplies of CuO nanorods under the contact surfaces and their rolling effect mechanism, which eventually leads to energy saving and prevents material loss.