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

• Published in: Macromolecules Vol. 34; no. 19; pp. 6649 - 6657
• Main Authors: Huang, Ping, Zhu, Lei, Cheng, Stephen Z. D, Ge, Qing, Quirk, Roderic P, Thomas, Edwin L, Lotz, Bernard, Hsiao, Benjamin S, Liu, Lizhi, Yeh, Fengji
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 11-09-2001
• Subjects: Applied sciences; Crystallization; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Properties and characterization; Polymer blends; Crystal orientation; Two dimensional system; Ethylene oxide copolymer; Experimental study; Cylindrical shape; Confined space; Structure processing relationship; Diblock copolymer; Styrene polymer; Homogeneous mixtures; Isothermal crystallization; Styrene copolymer
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma010671x

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 (T ODT) of this blend is 175 °C. Therefore, the PEO blocks form nanocylinders surrounded by a PS matrix below the T ODT. 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 (T c). At very low T c (<−30 °C), PEO crystals are randomly oriented within the confined cylinders. Starting at T c = −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 T c, and finally it becomes 90° when T c ≥ 2 °C. Crystallographic analysis indicates that the crystal c-axis orientation at each T c corresponds to a uniform crystal orientation.