Breaking the trade-off between oil film thickness and viscous friction – n-alcohol-containing lubricants in high-pressure contacts

Low-friction lubricant formulations are urgently needed to improve the energy efficiency of machines. Here, we show that blending 1-dodecanol with a hydrocarbon oil improves lubrication in non-conformal sliding/rolling contacts by simultaneously increasing hydrodynamic film thickness and reducing viscous friction. This is due to pressure-induced polymorphic phase transformations in the 1-dodecanol molecules after they flow through the film thickness-determining inlet and reach the load-supporting zone. At relatively low pressures, 1-dodecanol forms a lamellar hexagonal solid polymorph that gives durable superlubricity then, at higher pressures, it forms an orthorhombic polymorph. Both polymorphs cause anomalously low friction when blended into various hydrocarbon base oils over a wide range of speed, pressure, and shear rate conditions representative of rolling bearing and gear contacts. By breaking the ubiquitous trade-off between friction and film thickness, and enabling superlubricity, these blends pave the way for considerable energy efficiency improvements in widespread lubricated contacts.