Macromolecules, 34 (19), 6649 -6657, 2001. 10.1021/ma010671x S0024-9297(01)00671-4
Web Release Date: August 14, 2001

Copyright © 2001 American Chemical Society

Crystal Orientation Changes in Two-Dimensionally Confined Nanocylinders in a Poly(ethylene oxide)-b-polystyrene/Polystyrene Blend

Ping Huang, Lei Zhu, Stephen Z. D. Cheng,* Qing Ge, and Roderic P. Quirk

Maurice Morton Institute and Department of Polymer Science, The University of Akron, Akron, Ohio 44325-3909

Edwin L. Thomas

Department of Materials Science and Engineering, Massachusetts Institute and Technology, Cambridge, Massachusetts 02139

Bernard Lotz

Institute Charles Sadron, 6 Rue Boussingault, Strasbourg 67083, France

Benjamin S. Hsiao, Lizhi Liu, and Fengji Yeh

Department of Chemistry, The State University of New York at Stony Brook, Stony Brook, New York 11794-3400

Received April 17, 2001

Revised Manuscript Received July 2, 2001

Abstract:

A lamella-forming poly(ethylene oxide)-b-polystyrene (PEO-b-PS) diblock copolymer has been blended with a low molecular weight polystyrene (PS) homopolymer to form a miscible polymer blend. The PEO volume fraction is 0.32, and the order-disorder transition temperature (TODT) of this blend is 175 C. Therefore, the PEO blocks form nanocylinders surrounded by a PS matrix below the TODT. Since the glass transition temperature of the PS is 64 C and the PEO crystal melting occurs at ~50 C, the PEO-block crystallization takes place in a two-dimensionally confined glassy environment. The cylinder diameter is determined to be 13.7 nm, based on small-angle X-ray scattering (SAXS) and transmission electron microscopy results. Using simultaneous two-dimensional SAXS and wide-angle X-ray scattering techniques, the crystal orientation (the c-axes of the PEO crystals) within the nanocylinders is found to change simply depending upon the crystallization temperature (Tc). At very low Tc (<-30 C), PEO crystals are randomly oriented within the confined cylinders. Starting at Tc = -30 C, the crystal orientation changes to be inclined with respect to the cylinder axis, â. The tilt angle from â continuously increases with increasing Tc, and finally it becomes 90 when Tc 2 C. Crystallographic analysis indicates that the crystal c-axis orientation at each Tc corresponds to a uniform crystal orientation.

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