Abstract
The effects of temperature, pressure and shear stress on the viscosity of simplified automotive lubricants—polymer-thickened base oil solutions—were investigated. Various polymers—with different molecular weights and conformations (comb, linear and star)—were used at low concentration (1.2 % w/w) in a hydrocracked mineral base oil: a poly(alkylmethacrylate), an olefin copolymer and a poly(isoprene-styrene hydrogenated). Their rheological behavior was studied and modeled with a Vogel-Tamman and Fulcher equation, a modified Williams-Landel-Ferry-Yasutomi relationship and a Carreau-Yasuda-like formula. Then, the Einstein’s law was used to rapidly and simply determine the hydrodynamic radii of polymers as a function of temperature and pressure. Calculations from Flory equations, intrinsic viscosities and direct measurements confirmed the relevance of this methodology. Finally, molecular considerations allowed a good understanding of the rheological response of polymer solutions.
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