Carbon nanotube-based poly(ethylene oxide) nanocomposites

Abstract

Carbon nanotubes (CNTs) with their remarkable set of intrinsic properties are outstanding materials to incorporate in and augment the properties of polymer matrices. Poly(ethylene oxide) (PEO) is a water-soluble, biocompatible polymer that has found various technological applications including as solid electrolytes in lithium-ion batteries and in various biomedical and tissue engineering applications. Homogeneous dispersion of anisotropic nanoparticles, especially carbon nanotubes, in a matrix polymer is hindered by strong inter-tube attraction and a weak entropic driving force for the disruption of nematic order of such rodlike nanoparticles. In this chapter, we discuss different pathways to disperse carbon nanotubes in PEO matrix and techniques to quantitatively characterize the state of dispersion. Beyond the geometrical percolation threshold, in their quiescent state, dispersed nanotubes show hierarchical fractal network consisting of aggregated flocs. Internal to the flocs, individual or small bundles of nanotubes overlap each other to form a dense mesh. The inter-floc interaction dominates the linear visco-elasticity. The nonlinear viscoelastic behavior is independent of network size and dominated by cluster dynamics. Interestingly, significant changes in the melting and crystallization behavior of PEO along with a decrease in fractional crystallinity in the presence of carbon nanotubes have been observed. The observed changes significantly exceed those observed for an equivalent Li+ ion concentration mixture. This finding is particularly interesting considering amorphous segment of PEO chains are responsible for ion transport in solid polymer electrolytes. Besides this other technological applications of the carbon nanotube-based PEO nanocomposites will also be discussed.