Single-walled carbon nanotube-induced phase behavior of block copolymer systems

Abstract

For many practical applications of carbon nanotubes (CNTs), especially single-walled carbon nanotubes (SWNTs), the fabrication of SWNT superstructures with well-defined morphology, density, and direction is necessary to enhance the physical properties of SWNTs collectively or to create new functionalities. By utilizing the self-assembly of block copolymer, which shows rich phase behavior depending on the external conditions, such as concentration or temperature, we may achieve the fabrication of well-ordered SWNT superstructures in a simple and easy way. In this dissertation, as the first step toward this goal, the SWNT-induced phase behavior of block copolymer systems was studied and SWNT distribution was investigated using small-angle x-ray and neutron scattering. To the best of our knowledge, this is the first report of SWNT-induced lyotropic phase behavior study, so it can provide key information in the design of self-assembled SWNT superstructures. Among various kinds of Pluronic polymers (poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide), simply PEO-PPO-PEO), F108 (PEO130-PPO60-PEO130) and F127(PEO100-PPO70-PEO100) can be the best dispersant of SWNT due to the long PPO region (which helps stabilize hydrophobic interaction) as well as long PEO (which enables SWNT dispersion by facing water). By 1 hr tip sonication, the PPO of Pluronics can adsorb on the surface of exfoliated SWNT by hydrophobic interaction. After ultracentrifugation (4 hr, 110000 g) and decanting of upper ca. 70% solution, F108-SWNT and F127-SWNT solutions can be obtained that maintained their isolation condition for more than two months. After the redispersion process of both freeze-dried F108-SWNT and F127-SWNT in H2O, respectively, the stock solutions were divided into 20 conical tubes and evaporated to make 5 ~ 100 wt% concentration in a 5 wt% step. To observe the SWNT effect, F108-only and F127-only samples in aqueous solution were prepared using the same process. Using...