Forming Crystalline Polymer-Nano Interphase Structures for High-Modulus and High- Tensile/Strength Composite Fibers Jiangsha Meng, Yiying Zhang, Kenan Song, Marilyn L. Minus* PVA/single-walled nanotube (SWNT) composite fibers are fabricated using a steady shear-flow gel-spinning method. The resultant fibers show excellent tensile strength, modulus, and toughness of 4.9 GPa, 128 GPa, and 202 J  g 1 , respectively. Templated interfacial crystallization of PVA in the vicinity of SWNT is controlled by tailoring the degree of undercooling of PVA during the composite solution preparation. WAXD shows that the templated crystallization behavior of the PVA at the SWNT interfacial region is new. PVA/SWNT fibers that exhibit interfacial structure show a predominant crystalli- zation plane of (001) as compared to the (101) plane seen in PVA/SWNT fibers without a distinct interfacial structure. This demonstrates that the PVA interfacial region around SWNT has denser crystalline chain-packing. 1. Introduction The fabrication of polymer-based carbon nanotubes (CNT) reinforced fibers with high concentration of CNT (>10 wt%) has been a study of interest in recent years, motivated by the potential to produce composites with outstanding mechanical, electrical, and thermal properties. [1–12] Two main strategies are typically used to produce high- concentration CNT-based fiber: (i) solid-state spinning and (ii) solution-state spinning. For solid-state spinning processes, CNT fibers are spun by pulling CNT strands directly from CNT forests, [1,2] or from the CNT aerogels that are formed during growth in the chemical vapor deposition (CVD) reactor. [4,10] The mechanical performance of the resultant fibers strongly depends on the quality of the CNT source, as well as the fiber spinning process, and the post- spinning treatments. [13] It requires the nanotubes not only to be as long and as free of defects as possible, but also aligned along the fiber axis with great precision for the tubes to contribute to better axial properties in the fiber. However, the CNT length and defect control depends on the CNT synthesis processes. Additionally, CNT alignment in the fiber is affected by several mechanisms: (i) twisting processes during fiber spinning (i.e., which can misalign the J. Meng, Y. Zhang, K. Song, Prof. M. L. Minus Department of Mechanical and Industrial Engineering, Northeastern University, Boston MA 02115, USA E-mail: m.minus@neu.edu Full Paper ß 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Macromol. Mater. Eng. 2013, DOI: 10.1002/mame.201300025 1 wileyonlinelibrary.com Early View Publication; these are NOT the final page numbers, use DOI for citation !! R