Mapping Aging Effects on Polymer Surfaces: Specific Detection of Additives by Chemical Force Microscopy

We report in this contribution the successful application of chemical force microscopy to study aging of polymer surfaces at the submicroscopic scale. Adhesion force mapping using tips modified with methyl- and hydroxyl-terminated alkanethiols was used to probe the chemical composition of polypropylene surfaces as a function of aging time. We have measured adhesion force distributions on polypropylene melt-pressed films stabilized with antioxidants, process-stabilizing agents, and UV-light stabilizers. These adhesion force distributions were correlated with the additive distribution at the surface. We were able to evidence modifications of the local adhesion properties on the polymer surface due to material aging. These results support the conclusion that the UV-light stabilizer migrates toward the surface and forms a film that makes the surface less hydrophobic. Laterally resolved adhesion force maps show chemically heterogeneous surfaces on a sub-100 nm scale.