Preparation of crystalline polyimide nanofibers via solution crystallization

• Published in: Polymer journal 2023-06, Vol.55 (6), p.717-722
• Main Authors: Kumano, Shota, Takaki, Tomoyasu, Uchida, Tetsuya
• Format: Article
• Language: English
• Subjects: 639/301/357; 639/638/455/958; Biomaterials; Bioorganic Chemistry; Butanol; Chemistry; Chemistry and Materials Science; Chemistry/Food Science; Crystal morphology; Crystal structure; Crystallization; Dispersion; Drying; Heat treatment; Molecular chains; Molecular structure; Nanofibers; Polymer Sciences; Sulfuric acid; Surfaces and Interfaces; Thin Films; Unit cell
• ISSN: 0032-3896; 1349-0540
• DOI: 10.1038/s41428-023-00765-w

Two crystalline polyimide nanofibers (PINFs) with different morphologies were prepared. The crystalline unit cells of the aromatic PI crystals and the crystal morphologies of the fabricated PINFs were examined. PINF-I (lengths = 305 ± 152 nm and diameters = 12 ± 2 nm) was crystallized from crystalline PI dissolved in a concentrated sulfuric acid solution. The resulting PINF-I was isolated from this solution, and it did not aggregate in water. PINF-II with diameters of 105 ± 99 nm was prepared by dispersing PINF-I in a mixed water and t- butanol (TBA) solution (water:TBA = 4:1), followed by freeze-drying. Then, the PINF-II was heated to enhance its crystallinity. X-ray diffraction and transmission electron microscopy studies of the heat-treated PINF-II revealed a PI crystalline unit cell [orthorhombic, a  = 1.21 nm, b  = 0.88 nm, and c  = 2.23 nm (molecular chain axis direction)]. The crystal structure of the heat-treated PINF-II suggested that highly crystalline PINFs were fabricated in which the PI molecular chains were oriented along the direction of the fiber lengths. Two types of polyimide nanofibers (PINFs) were prepared. PINF-I (lengths = 305 ± 152 nm and diameters = 12 ± 2 nm) was prepared via crystallization of PI dissolved in a concentrated sulfuric acid solution. Adding t -butanol to a PINF-I aqueous dispersion and subsequent freeze–drying produced PINF-II (diameters = 105 ± 99 nm) with PINF-I aggregated into a fibrous form. The PI crystalline unit cell parameters were orthorhombic, a  = 1.21 nm, b  = 0.88 nm, and c  = 2.23 nm (molecular chain axis direction).