A novel method for well-organized polystyrene-grafted multi-walled carbon nanotube bundles via self-assembly in tetrahydrofuran

Polystyrene (PS) grafted multi-walled carbon nanotubes (MWCNTs) were well-organized as bundles by a selfassembly method in tetrahydrofuran (THF). PS was synthesized by atom transfer radical polymerization and grafted to the surface of tubes through covalent bonds. Unmodified tubes agglomerated irregularly and precipitated instantly because of poor compatibility with THF. But soluble PS provides solvent-phobic MWCNTs with suspending stability and dispersibility in the dispersant. Therefore, MWCNT-g-PS has amphiphilic property in this selective solvent and owns ability to self-assemble. Scanning and transmission electron microscope images show that self-assemblies (SAs) are columnar with a tight and ordered head and a loose tail. Their length ranges from 15 to 25 µm while width from 1.5 to 4 µm. In these super structures, tubes are regular organized and parallel arranged. Because MWCNT-g-PS has a huge rigid rod-core and multi-flexible-armed structure in the suspension, a novel micro-phase separation model is proposed to explain this behavior. There are two kinds of micro-phase separation locating on two mutual perpendicular faces on tubes. Solvent-philic/solvent-phobic interaction plays a key role in self-assembly. Moreover, a balance between buoyancy and gravity on SAs decides whether this process is finished or not.