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Published January 29, 2002 | public
Journal Article

Orientational Proliferation and Successive Twinning from Thermoreversible Hexagonal−Body-Centered Cubic Transitions


The deterministic proliferation of the orientation of hexagonally packed cylinders (HEX) from the twinned body-centered cubic (BCC) phase is investigated by synchrotron small-angle X-ray scattering (SAXS) and rheo-optical methods for di- and triblock copolymers of styrene and isoprene (SI and SIS). Repeated heating and cooling cycles starting from an initially aligned HEX produce a proliferation of cylinder orientations from successively twinned BCC states. The evolution of the orientation distribution of HEX cylinders produces a decrease in the birefringence and increase in the modulus with each successive generation. The cylinder axes of the degenerate HEX states coincide with the 〈111〉 directions of the twinned BCC due to the epitaxial growth of cylinders from the twinned BCC. The distribution of the cylinder axes of the degenerate HEX states among the 〈111〉 directions of the twinned BCC is found to be affected by memory of the prior HEX state, which decays with annealing time in the BCC state.

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© 2002 American Chemical Society. Received 31 May 2001. Published online 3 January 2002. Published in print 1 January 2002 We acknowledge helpful discussions with Professors T. Hashimoto, T. Lodge, S. Okamoto, C. Y. Ryu, S. Sakurai and A. C. Shi. This work was supported by KOSEF (97-05-02-03-01-3), by the Applied Rheology Center governed by KOSEF (2000 G0202), by TND projects supported by the Ministry of Science and Technology (MOST) and by NSF (CTS-9729443) and AFOSR (LC MURI). Synchrotron SAXS at the PLS (3C2 and 4C1 beam lines) was supported by MOST and Pohang Iron and Steel Co. (POSCO). Vector 4111 was kindly provided by Professor C. D. Han at the University of Akron.

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