Transition of liquid crystal anchoring at the microdomain interface observed for main-chain nematic polyester segments of block copolymers

• Published in: Polymer journal Vol. 51; no. 2; pp. 295 - 302
• Main Authors: Koga, Maito, Wakabayashi, Takumi, Kang, Sungmin, Tokita, Masatoshi
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.02.2019; Nature Publishing Group
• Subjects: 140/131; 639/301/923/1028; 639/301/923/919; Anchoring; Biomaterials; Bioorganic Chemistry; Block copolymers; Chains; Chemistry; Chemistry and Materials Science; Chemistry/Food Science; Crystal structure; Lamellar structure; Liquid crystals; Original Article; Polyesters; Polymer Sciences; Polystyrene resins; Segments; Small angle X ray scattering; Surfaces and Interfaces; Thickness; Thin Films
• ISSN: 0032-3896; 1349-0540
• DOI: 10.1038/s41428-018-0131-x

The microdomain structures and liquid crystal (LC) orientations of ABA triblock copolymers comprising poly(styrene) (PS) A blocks and a main-chain LC polyester B block were examined via small-angle X-ray scattering and electron microscopy in the form of fibrous samples. The LC polyester blocks were segregated from the PS blocks to form a nematic LC in the lamellar microdomains of the copolymers, with the PS volume fraction ( φ ) ranging from 13 to 38%. As φ decreased, the nematic director was always positioned along the fiber axis, but the microdomain lamellae changed their direction from parallel to perpendicular with respect to the fiber axis and began to adopt a zigzag configuration. These lamellar orientations were attributed to the main-chain nematic LC segments lying along the microdomain interface but extending perpendicularly to the interface as the occupying interface area was reduced. The lamellar microdomains parallel to the nematic director increased the LC and PS lamellar thicknesses reversibly by 48 and 16%, respectively, at the same time as the isotropization of the nematic LC. Such changes in lamellar thickness suggest that both the PS and LC segments were elongated along the direction of the LC orientation. Lamellar microdomain and liquid crystal (LC) orientations in a fibrous sample were investigated for a series of ABA triblock copolymers comprising poly(styrene) (PS) A blocks and a main-chain nematic LC polyester B block. As the PS volume fraction decreased from 38 to 13%, the lamellae changed their direction from parallel to perpendicular with respect to the fiber axis and began to adopt a zigzag configuration, although the LC mesogens always lay along the fiber axis. At the microdomain interface, the LC mesogens exhibited an anchoring transition from planar to homeotropic.