Structural Evolution in Polymer Nanocomposite Fibers—A Molecular Dynamics Simulation Approach

Abstract

Carbon nanotube (CNT)-based polymer nanocomposites have often been processed into fibers because fibrous shapes are one of the best methods of fully exploiting the anisotropies and structures of CNTs. Among various types of polymer-CNT nanocomposite fiber, polyacrylonitrile (PAN) has been among the most studied polymeric system because it strongly interacts with CNTs and is the most common source of high-performance carbon fibers. In order to understand the structural evolution and related mechanical properties under extensional flow, molecular dynamics (MD) simulations were performed on polyacrylonitrile–single-wall carbon nanotube (PAN-SWNT) nanocomposites, to a draw ratio of two, which mimics fiber-spinning and drawing processes. Two SWNT(5,5)- and SWNT(10,10)-containing nanocomposite systems, as well as a control PAN, were constructed. Higher stresses were observed in both nanocomposite systems. In addition, higher Young’s (4.76 GPa) and bulk (4.09 GPa) moduli were observed when the smaller-diameter SWNT(5,5) was used, compared to those of PAN-SWNT(10,10) (4.41 GPa and 3.96 GPa, respectively), suggesting that SWNT(5,5) resists stress better. Furthermore, we also observed the formation of void structures at both ends of the SWNTs, especially for the large-diameter SWNT(10,10); these voids became larger in the drawing direction with increasing draw ratio and may adversely affect the mechanical properties of the nanocomposite fibers.