Evanescent wave optics to study diffusion in polymers at interfaces

Diffusion processes in polymers are important in many applications such as coatings, sensor devices, fuel cells and drug delivery. To understand the transport processes in these applications, the role of the interface becomes more important. The affinity of the polymer chains to the interface proves to be crucial. Surface plasmon resonance and optical waveguide spectroscopy can be used to determine the optical density, diffusion of gas and orientation of polymer chains at interface and bulk in a single measurement. Therefore different metal-enhanced waveguide sensors have been developed and evaluated. We could show that the penetration of molecules into a polymer film by diffusion gives rise to reversible refractive index changes. We have investigated films from amorphous fluoroploymers on different metal-coated interfaces and observed clear differences in the interphase close to the interface but not in the bulk.