Interfaces in self-assembling diblock copolymer systems: Characterization of poly(isoprene-b-methyl methacrylate) micelles in acetonitrile

The kinetics of dipolar nonradiative energy transfer (DET) between dyes con fined to the core-corona interface region of poly(isoprene-b-methyl methacr ylate) block copolymers (PI-PMMA) in acetonitrile was analyzed using a new distribution model for energy transfer in spherical micelles. The distribut ion of block junction points was described by the model of Helfand and Taga mi (HT) for the strong segregation limit, adapted for the spherical geometr y of the core-corona interface. We used this model to analyze experimental fluorescence decay curves for block copolymer micelles made up of polymers containing a donor dye or an acceptor dye covalently attached to the PI-PMM A junction. The analysis yielded an interface thickness between the PI core and the PMMA corona of delta = (0.9 +/- 0.1) nm. In the past, the experime ntal fluorescence decay curves measured for similar systems have been fitte d with the Klafter and Blumen (KB) equation for energy transfer, which has a stretched exponential form. To relate these results to topological charac teristics of the system, we simulated donor decay profiles for different in terface thickness values using the new distribution model for energy transf er and a modified HT equation. Subsequent analysis by the stretched exponen tial KB equation proved that the magnitude of the fitted exponent is direct ly related to the interface thickness between the blocks for a given dye co ncentration in the core-corona interface. Within a certain range of interfa ce thickness values, this relation can be used to determine the interface t hickness from the fitting parameters of the KB equation.