INTERFACIAL CURVATURE IN GRAFT AND DIBLOCK COPOLYMERS AND IMPLICATIONS FOR LONG-RANGE ORDER IN CYLINDRICAL MORPHOLOGIES

Microstructures of block copolymers in the strong segregation limit ar e characterized by well-defined interfaces separating the different bl ock materials into domains on a nanometer scale. In this paper, we add ress the effects of architectural and conformational asymmetry of the blocks on the interfacial curvature characteristics and on the degree of long-range order in the cylindrical morphologies. Experimental (TEM and SAXS) curvature data from polyisoprene-polystyrene (I2S) simple g raft block copolymers and from polyisoprene-poly(tert-butyl methacryla te) (PtBMA) linear, conformationally asymmetric diblock copolymers are presented and compared to data from polyisoprene-polystyrene linear d iblock copolymers. The experimental data are elucidated by a simple cu rvature free energy model which accounts for core-space-filling withou t explicitly specifying the shape of the microdomain. This model allow s the prediction of preferred interfacial curvature characteristics as a function of molecular architecture. Good agreement is obtained betw een the theoretically calculated mean and Gaussian curvatures and the experimentally measured values. A key finding is that the degree of fr ustration, as measured by the difference between the free energy of th e preferred curvature of a given block copolymer and that of the neare st accessible space-filling structure (such as the cylindrical structu re), is correlated with the degree of long-range order.