Study of polymer diffusion across the interface in latex films through direct energy transfer experiments

Efforts have been made to improve the method of using direct nonradiative energy transfer to follow the interdiffusion of polymer molecules across an interface. Two data analysis techniques are developed. The first one presents the extent of interdiffusion in terms of an acceptor concentration distribution; the second one recovers the diffusion coefficient and the concentration profile based on a Fickian diffusion model. The first method is model independent while the second method can be readily extended for other diffusion models. Polydisperse systems are characterized by a distribution of molecular mobilities. The energy transfer experiment provides a mean diffusion coefficient averaged over the sample history. For such systems, the concept of ‘‘instantaneous’’ effective diffusion coefficient and a method to derive it are discussed. These techniques are examined using computer simulations and tested in the study of molecular diffusion process of a poly(butyl methacrylate) latex system.