Polymer films are often produced from aqueous polymer dispersions. Polymer dispersions consist of polymer nanoparticles in water. The filming of drying polymer dispersions takes place in three stages: water evaporation, particle deformation and polymer interdiffusion. Polymer interdiffusion is necessary to form a homogeneous film with sufficient cohesion. In this step, polymer chains diffuse into neighboring particles, the particle boundaries disappear and an entanglement network is formed.

The research group uses Förster resonance energy transfer (FRET), a fluorescence method, to track interdiffusion. We are currently investigating interdiffusion in water-based pressure-sensitive adhesives in collaboration with BASF SE. Pressure-sensitive adhesives consist of soft, slightly cross-linked polymers. In order to increase cohesion, the chains are ionically cross-linked during film formation. Ionic cross-linking is fundamentally reversible, which makes it possible to develop self-healing materials. FRET measurements were used to demonstrate interdiffusion; crosslinking in the dry film was verified by mechanical measurements.