Synergistic effects of functionalized h-BN and ionic liquid on tribological performance and thermal stability of PAO-based nanolubricants

This study investigates the tribological properties and thermal stability of a novel hybrid nanolubricant composed of pristine hexagonal boron nitride (BN), functionalized hexagonal boron nitride (fBN) nanosheets, and anionic liquid (IL) as additives, with polyalphaolefin (PAO) as the base oil. The microstructural and chemical characteristics of pristine BN and fBN were characterized by XRD, HR-SEM, HR-TEM, FTIR, and Raman spectroscopy.Nanolubricants were prepared by blending of BN and fBN at 0.05 wt% and 0.1 wt% concentrations, and IL at a fixed 1 wt%, into PAO base oil. Tribological testing was conducted using a “ball-on-disc” setup, while thermal stability was assessed via thermo-gravimetric analysis (TGA). Thermal stability improved significantly, with the onset degradation temperature increasing by approximately 33 % and the complete decomposition temperature rising by 21 % compared to neat PAO. The formulation containing 0.1 wt% fBN and 1 wt% IL in PAO exhibited the maximum reduction in COF (approximately 61 %) and wear volume (approximately 33 %). The performance improvements are attributed to tribo-film formation at contact interfaces, confirmed by HR-SEM, EDX, 3D optical profilometry, and Raman spectroscopy. The novelty of this work lies in the synergistic integration of functionalized BN nanosheets with an imidazolium-based IL in a nonpolar PAO base oil, which has not been explored previously. This hybrid formulation substantially enhanced friction reduction and wear resistance under boundary lubrication, providing a promising pathway for developing advanced nanolubricants to improve energy efficiency and extend component durability.