Non-uniform composition profiles in thin film polymeric nanofoams

Neutron reflectivity (NR) and dynamic secondary ion mass spectroscopy (DSIMS) were used to study compositional variations as a function of film depth in thin polymeric nanofoam films formed from triblock copolymers containing 15 wt%, 13 kg/mol polypropylene oxide end blocks with a fluorinated polyimide center block. The triblock copolymer films were spun cast and imidized on silicon substrates and showed an excess amount of polyimide present at both the air/film and film/substrate interfaces. Upon foaming the films showed a slight densification, and the formation of a 50- 150 Å thick polyimide skin at the air interface. The final nanofoam materials had a calculated porosity of roughly 20 vol.% in the center portion of the film. (C) 1999 Elsevier Science Ltd.