Pressure viscosity coefficient of lubricant base oils as estimated by nuclear magnetic resonance spectroscopy

The pressure viscosity coefficient (PVC) is an important parameter for base oils in defining their lubricating capacity because it reflects the extent of "thickening" that occurs under high hydrodynamic loads. In this study, spin-lattice relaxation times (T₁) derived from NMR experiments are used to probe the dynamic motional environment for a series of compositionally different base oils to better understand the relationship between chemical structure and bulk physical properties such as viscosity and PVC. Using a multivariable statistical analysis, it was demonstrated that the T₁ times for certain ¹³C NMR resonances combined with the viscosity index can accurately predict the PVC of a base oil (R² = 0.99). Further, ¹³C NMR-derived "average structural parameters" including certain paraffin, isoparaffin, and naphthenic structures, also predicted PVC very accurately (R² = 0.99). Collectively, these results illustrate that the "energy-conserving" and "traction" properties of lubricants can be predicted from the dynamics and structure of base oil molecules at ambient temperatures and pressures.