Rheology of olefinic copolymer layers adsorbed on solid surfaces

The rheology of two adsorbed layers of olefinic copolymers (OCPs) between two cobalt surfaces was investigated using a surface force apparatus (SFA). Each polymer layer is obtained by adsorption in a dilute solution of OCP and dispersant OCP (DOCP) in a 175 neutral solvent basestock at 24 degrees C. The aim of these experiments is the mechanical characterization of the compressed polymer films. The hydrodynamic thickness L(H) detected is compared with the thickness of the polymer layers L and the hydrodynamic radius R(H) of the polymer coil in solution. All these distances, strongly related to the chemical structure of the polymer, indicate that the layers are not always homogeneous. For OCP, 0.55L approximate to L(H) approximate to 2R(H), and for DOCP L approximate to L(H) approximate to 2.7R(H). Finally the two layers present different inelastic behaviors. The DOCP layer presents a mesh more compact and more uniform than the OCP layer as indicated by the thickness measurements.