A Microscopic Study by Dynamic Light Scattering of Four Viscosity Index Improvers in Two Model Solvents and a Mineral Base Oil

Four polymeric viscosity index improvers [PAMA: poly(n-alkyl methacrylate), EP: (ethylene-propylene) copolymer, HPI: hydrogenated poly(isoprene) polymer and SHB: (styrene-hydrogenated butadiene) copolymer], are studied in cyclohexane, n-heptane and a mineral base oil (130 NS). The hydrodynamic diameter of isolated and aggregated polymers is measured by Dynamic Light Scattering technique.

The sample concentrations were always below C* which is the concentration of first overlap separating the dilute regime from the semi-dilute regime. Experiments were run from 20 to 90°C.

Our results show that, depending on the chemical nature of the polymer, the solvent and the temperature value, the solute particles are either aggregated (micelles or not) or isolated.