(230c) High Pressure Viscosity of Poly(alpha olefin)s

Synthetic oils composed of poly(alpha olefins) are a class of base oils that are important in the formulation of automotive lubricants. They are often modified with additives that may incorporate polar or non-polar groups to improve their performance.

In this study, the densities and viscosities of mixtures of a low viscosity synthetic oil with both polymeric and micelle forming additives were determined as a function of temperature, pressure and, in the case of viscosity, shear rate. To determine viscosity as a function of pressure, a novel high-pressure rotational viscometer has been developed in our laboratory. The viscometer consists of an inner rotating shaft with an imbedded magnet which permits its coupling with an external rotating magnet. The external magnet is part of a torque measurement unit, which allows determination of torque as a function of pressure/ temperature /rotational speed the oil experiences inside a high-pressure chamber. The viscometer is also equipped with a variable volume part housing a movable piston, which allows changing the internal volume and thus the pressure. The viscometer main cell is also equipped with sapphire windows to assess the phase state of the oil at the experimental conditions.

In this talk, we will present the results of viscosity measurements and volumetric determinations and their modeling with Sanchez-Lacombe equation of state and the free volume theory of viscosity using the experimental data collected at temperatures up to 100ËšC and 40 MPa at rotational speeds up to 800 rpm.