Self-assembled ordering of single-walled carbon nanotubes in a lyotropic liquid crystal system

Abstract

We have carried out small angle X-ray scattering (SAXS) studies as a function of temperature on 0.01 wt.% single-walled carbon nanotubes (SWCNTs) dispersed lyotropic liquid crystal (LLC) system consisting of 25 wt.% cetyltrimethylammonium bromide (CTAB) in water. This LLC system exhibits crystalline surfactant + water (Cr), nematic (N), hexagonal (H) and isotropic (I) phases on heating. Our SAXS pattern revealed that in the crystalline + water phase of the LLC, the doped CNTs exhibit 1-D ordering. In the nematic and hexagonal phases of the LLC, the CNTs exhibit 2-D hexagonal ordering. In the isotropic phase, there are domains of CNTs and within each domain, the nanotubes exhibit 1-D ordering. A plot of d-spacing of the CNTs as a function of temperature showed peaks at the phase transition temperatures of the LLC. We have also carried out optical birefringence and electrical conductivity measurements of the composite as a function of temperature. Interestingly, they also showed peaks at the phase transition temperatures. This indicates a correlation between the d-spacing of the CNTs and the anomalous increase in the birefringence and conductivity of the composite at the phase transition temperatures.