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Published November 3, 1997 | public
Journal Article

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 are characterized by well-defined interfaces separating the different block materials into domains on a nanometer scale. In this paper, we address 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 graft block copolymers and from polyisoprene−poly(tert-butyl methacrylate) (PtBMA) linear, conformationally asymmetric diblock copolymers are presented and compared to data from polyisoprene−polystyrene linear diblock copolymers. The experimental data are elucidated by a simple curvature free energy model which accounts for core-space-filling without explicitly specifying the shape of the microdomain. This model allows the prediction of preferred interfacial curvature characteristics as a function of molecular architecture. Good agreement is obtained between the theoretically calculated mean and Gaussian curvatures and the experimentally measured values. A key finding is that the degree of frustration, as measured by the difference between the free energy of the preferred curvature of a given block copolymer and that of the nearest accessible space-filling structure (such as the cylindrical structure), is correlated with the degree of long-range order.

Additional Information

© 1997 American Chemical Society. Received March 14, 1997; Revised Manuscript Received September 2, 1997. Publication Date (Web): November 3, 1997. We wish to acknowledge Darrin J. Pochan for providing TEM and SAXS data for this paper and Chin Lee for useful discussions. S.P.G. acknowledges funding from the Army Research Office in the form of an Army Young Investigator Award DAAH04-95-I-0305. Use of TEM instrumentation in the W. M. Keck Electron Microscopy Laboratory at the University of Massachusetts-Amherst is acknowledged, as is the use of central facilities of the Materials Research Science and Engineering Center (MRSEC) at the University of Massachusetts. Z.-G.W acknowledges support from the National Science Foundation (Grant Nos. ASC-9217368 and DMR-9531914), the Camille and Henry Dreyfus Foundation (Award No. TC-96-063) and the Alfred P. Sloan Foundation (Award No. BR-3508).

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