Lyotropic Liquid Crystal of Polyacrylonitrile-Grafted Graphene Oxide and Its Assembled Continuous Strong Nacre-Mimetic Fibers

Abstract

Liquid crystals (LCs) of pristine graphene oxide (GO), a kind of novel two-dimensional (2D) macromolecule, have been discovered recently, opening an avenue to high performance neat graphene fibers. Here, we report for the first time LC of polymer-grafted GO and its macroscopic assembled nacre-mimetic composite. Polyacrylonitrile (PAN) chains were covalently and uniformly grafted onto GO surfaces via a simple free radical polymerization process. The PAN-grafted GO (GO - g - PAN) sheets were well dispersed in polar organic solvents such as dimethylformamide (DMF) and dimethyl sulfoxide (DMSO), forming nematic and lamellar LCs upon increasing concentration. A strong signal was found in the circular dichroism spectra of the LCs, indicating the formation of helical lamellar structures for the GO - g - PAN LCs. Macroscopic assembled fibers were continuously spun from the GO - g - PAN LCs via the industrially viable wet-spinning technology. The fibers held strict layered structures of GO and PAN, resembling the classic “brick-and-mortar” microstructure observed in nacre. The nacre-mimetic composite showed excellent mechanical property with tensile strength of 452 MPa, Young’s modulus of 8.31 GPa, and breakage elongation of 5.44%. This offers a new approach for the fabrication of continuous, ultrastrong, and tough biomimic composites.