Classical mean-field treatments of block copolymer phase behavior have been remarkably successful at accounting for most of the states of microphase separation in relatively high molecular weight AB diblock and certain ABC triblock copolymer melts. However, in order to obtain smaller domain dimensions the overall molecular weight must be reduced while simultaneously increasing the magnitude of the Flory-Huggins segment-segment interaction parameters. In this limit the assumptions of weak segregation and Gaussian coil statistics are compromised even near the order-disorder transition. We have investigated block copolymer melts comprised of relatively strongly incompatible blocks such as poly(isoprene) and poly(lactide) using small-angle x-ray scattering, dynamic mechanical spectroscopy, TEM and DSC. A new ordered arrangement of spherical domains, denoted the sigma-phase, and evidence of strong composition fluctuations in the disordered state as a function of the molecular composition, will be described.* Research was conducted in collaboration with Sangwoo Lee, Jingwen Zhang, and Timothy Gillard from the University of Minnesota.

Strongly segregated block copolymers near the order-disorder transition

243rd National Meeting (2012)

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