The Temperature Dependence of Divergence Pressure

The so-called controversy in elastohydrodynamic lubrication (EHL) regarding the nature of the shear dependence of viscosity, Eyring versus Carreau, is truly a controversy regarding the pressure and temperature dependence of low-shear viscosity. Roelands removed data that contradicted his claims of accuracy for his correlation. The Roelands hoax became acceptable in EHL because ignoring the universal previtreous piezoviscous response made the traction calculated with the Eyring assumption appear to be reasonable. Traction and minimum film thickness calculations sometimes require the description of viscosity at pressures up to the glass transition pressure. There have been few measurements of viscosity at pressures up to glass pressure. Therefore, a need exists for a piezoviscous model that extrapolates accurately, and the Hybrid model fills that need. Here, an improved relation for the temperature dependence of divergence pressure is offered and extrapolation is demonstrated for a polyalphaolefin and propylene carbonate. A linear dependence of divergence pressure with temperature is more useful than previous versions. An improvement in the capability of high-pressure viscometry is suggested based upon the fractional Stokes Einstein Debye relation and the relatively simple measurements of DC conductivity.