The Microstructure of Calcium Sulfonate Complex Lubricating Grease and Its Change in the Presence of Water

Calcium sulfonate complex grease is often selected for rolling bearing lubrication if there is a risk for water ingress, because it is reported throughout literature that it can absorb large quantities of water. In this article, atomic force microscopy (AFM) measurements have been performed on a commercially available grease with and without water to investigate the microstructural change under the influence of water. From the results it is clear that the formation of large (inverted) micelles, which can be up to a few micrometers in diameter, is the main mechanism responsible for the absorption water. These results can be used to explain the earlier reported effect of water on the rheological and lubricating properties of these grease types. It is shown here that the size distribution of the micelle structure is a function of the amount of water mixed into the bulk grease.