Interdiffusion in Polymeric Multilayer Systems Studied by Inverse Micro-Raman Spectroscopy

Interdiffusion is likely to occur if two miscible polymeric films are in contact with each other in the presence of a solvent. This is e.g. relevant for the production of organic light-emitting diodes (OLEDs). Interdiffusion in OLED multilayer stacks has a great influence on the device performance. Yet, there is no study monitoring these interdiffusion processes. This is essential to gain fundamental knowledge about the predominant parameters influencing mass transfer between the present solids. In this work we demonstrate the application of inverse micro-Raman spectroscopy (IMRS) for in situ measurement of interdiffusion in polymeric multilayer systems. Interdiffusion only occurs in miscible systems, whereas no intermixing of the polymers occurs in immiscible systems. Given a miscible system, the average solvent content was found to be more important than the molecular weight of the polymers for the interdiffusion kinetics.