Understanding the physical structure of greases can provide critical insight into improving the lubricating performance of a grease. Observation of the grease structure can be quite difficult depending on the type of grease and the length scale of the structure. Polyurea greases in previous reports have typically been examined by removal of the oil phase, which significantly changes the polyurea structure. This paper examines the effect of sample preparation conditions on the microstructure of polyurea greases. This study reveals new structures in the polyurea that have not been observed in the previous literature, including entangled fibers and nanotubes. Correlation is found between the observed polyurea microstructure coverage and grease stiffness.
Keywords: TEM; cryo-SEM; grease; nanotubes; polyurea; tomography; ultramicrotomy.