Conformational Dynamics of Block Copolymer Liquids

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Block copolymers enjoy increasing use in a wide range of materials applications, due primarily to properties derived from the thermodynamic interactions between blocks. With increasing chain length and/or interaction strength, block copolymer liquids undergo an order-disorder transition (ODT) to a microstructured state. Although much has been learned about the accessible morphologies in the strong-segregation limit, i.e., well into the ordered state, the behavior in the vicinity of the ODT, i.e., the weak-segregation limit, is much less understood. We will use a powerful optical technique, oscillatory flow birefringence (OFB), to both diagnose and characterize the ODT and associated order-order transitions. In addition, extensive calculations have shown that the dilute- solution OFB properties of block copolymers are uniquely sensitive to the lengths and chain locations of the various blocks; both quantities are otherwise difficult to determine. We will explore the potential of OFB as a characterization tool for block copolymers, and in so doing assess the effect of the block-block interaction on the relaxation spectrum. Finally, the investigation will be continued of the role of the solvent in conformational dynamics experiments such as OFB, both in terms of solvent dynamics and solvent quality. In particular, a remarkable relationship between solvent rotational relaxation and the high-frequency viscoelastic properties of polymer solutions will be examined further.