Energy Transfer Study of the Interface Thickness in Symmetrical Isoprene−Methyl Methacrylate Diblock Copolymers

Abstract

We describe direct nonradiative energy transfer (DET) experiments on mixtures of two symmetrical poly(isoprene-b-methyl methacrylate) block copolymers of similar molar mass and composition, bearing different dyes at the junction. One polymer has a donor dye (9-phenanthrene) at the junction, and the other has an acceptor dye (2-anthracene). Small-angle X-ray scattering experiments show that films of the mixed diblock copolymers have a lamellar morphology with a spacing that varies with composition from 24 to 26 nm. Fluorescence decay profiles from these films were analyzed in terms of an energy transfer model that takes account of the distribution of junctions across the interface. On the basis of the value R0 = 2.3 nm for the characteristic ET distance and an assumed value of 〈κ2〉 = 0.476 for the preaveraged orientation parameter for randomly oriented immobile dipoles, we calculate an interface thickness of 1.6 ± 0.1 nm. This value is independent of the acceptor/donor ratio (i.e., the acceptor concentration) in the films.