Effective Volume per Junction in Block Copolymer Interfaces Probed by Direct Energy Transfer

Direct nonradiative energy transfer (DET) experiments were carried out on a series of labeled polyisoprene−poly(methyl methacrylate) (PI−PMMA) and polystyrene−poly(methyl methacrylate) (PS−PMMA) diblock copolymers spanning a range of molecular weights and compositions. In all samples with spherical or cylindrical morphology, PMMA represents the major component, with PI or PS microdomains dispersed within the PMMA phase. These DET experiments yield the ratio of the microdomain size R to the interface thickness δ. We relate the R /δ ratio to the volume per junction v j at the block copolymer interface and show that v j does not depend upon the microdomain geometry or the overall block copolymer molecular weight, but only on the length N B of the shorter component. We derive an expression which accommodates the observed dependence of v j on N B 1/3 .