The relationship between structural change of thickeners and rheological properties on lubricating grease

Lubricating grease shows the typical rheological properties, such as yield stress, shear thinning and thixotropy. These properties are believed to be originated by changes of thickener structure of grease, though the relationship between the structural change and grease rheology is not fully understood. This study investigates this relationship using lithium 12-hydroxy stearate greases and lithium stearate greases with different thickener concentration, penetration, base oil type, and prototype methods. Rheological property with two pre-shear conditions was evaluated, and thickener structure of greases were observed using an optical microscope, SEM and AFM. Orientation of thickeners and dispersion of thickener aggregations induced by shear were observed using AFM. In addition, it is shown wettability of base oil on thickeners depends on thickener types.