Lubrication Properties of Polyalphaolefin and Polysiloxane Lubricants: Molecular Structure–Tribology Relationships

Elastohydrodynamic lubrication properties and friction behaviors of several ester base stocks

“…This is partly due to the flexibility of the oleate group. A similar phenomenon was also found for polymerized polydimethylsiloxanes (PDMS) [5]. In general, a higher activation energy corresponds to a stronger dependence of viscosity on temperature, suggesting a low viscosity index (VI).…”

“…The system uses a polished AISI 52100 steel ball of 19.050 mm diameter, which is pressed, under 20 N load, against an optically transparent glass disk coated with a 500 nm thick silica spacer layer. The respective Young's moduli of the glass disk and steel ball are 75 and 210 GPa, giving a maximum Hertzian pressure of 0.54 GPa [5,22]. The root mean square (RMS) roughness values of the glass disks and steel balls are about 5 and 14 nm, respectively, giving a composite roughness of about 15 nm.…”

“…The ball velocity was varied from 0.025 to 5.00 m/s. The friction measurements were done at  = 0.50 and  = 1.00 [5].…”

“…(3)) describes the temperature dependence of viscosity, where  R is the low shear viscosity at infinite temperature,  G is the activation energy for a viscous flow, resulting from the movement of an "activated" molecule from one equilibrium position to another in the preferred direction of shear; treated as a jump over a potentialenergy barrier [33]. R is the universal gas constant, and T is the operating temperature [5,34]. The activation energy for various lubricants can be thus obtained from the viscosity data over the whole temperature range of interest through a non-linear regression, and the results are also given in Table 1.…”

“…The high Hertzian pressures in many tribological interfaces can cause elastic deformation and flattening of asperities in the regime of elastohydrodynamic lubrication (EHL) and mixed lubrication, which can occur in gears, rolling element bearings, cams and followers, continuously variable speed drives, and rail-wheel contacts, etc [5,6]. The optical film thickness measurement is widely employed to evaluate the lubrication properties of a fluid via measuring EHL film thickness [7−10].…”