Effect of Polyisobutylene on the Volumetric Properties and Viscosity of a Poly(α-olefin) Base Oil

Polyisobutylene (PIB) is the hydrocarbon backbone of the common dispersant additives in automotive lubricants. This study reports on the effect of PIB on the volumetric properties and viscosity of a synthetic poly(alpha-olefin) base oil, PAO 4. Addition levels of 1, 2, and 5 wt % have been evaluated for PIBs with molecular weights of 950, 1986, and 18,000 g/mol. Evaluations were conducted over a pressure range from 10 to 40 MPa at 298, 323, 348, 373, and 398 K. The density data were correlated with the Sanchez-Lacombe equation of state which were then used to evaluate compressibility, expansivity, and internal pressure. The density correlations were further used in correlating the viscosity in terms of the free-volume and density-scaling theories. The results are discussed in terms of the possible changes that PIB may cause in the packing of the base oil and the changes that are observed in the dissipative length, free-volume overlap, diffusive energy barrier, and density scaling parameter of the base oil.

Automated summary

This study investigates the impact of polyisobutylene (PIB) on the volumetric properties and viscosity of synthetic poly(alpha-olefin) base oil. Experimental evaluations were conducted to examine the effects of different molecular weights and addition levels of PIB on the base oil. Correlations between density and viscosity were analyzed to understand the changes caused by PIB. The results provide insights into the alterations in the base oil's packing and other parameters induced by PIB.