Water-redispersible single-walled carbon nanotubes and their self-assembled ordered superstructures in polymeric systems

Abstract

We develop individually isolated SWNTs (p-SWNT) that are easily redispersible in water by only 10 minutes of mild vortex mixing to overcome the insolubility and bundling problems of SWNTs in solutions, and investigate their self-assembled superstructures in three different polymeric systems (P84/water/pxylene ternary system, PE6200/water binary system, and PE6400/water binary system) by small angle neutron and x-ray scatterings (SANS and SAXS) measurements. To our knolwedge, this is the first demonstration of self-assembled orderd SWNT superstructures using the rich phase behavior of polymeric systems. The p-SWNTs are achieved by 1) dispersing SWNTs in water using cationic surfactant, cetyltrimethylammonium 4-vinylbenzoate (CTVB), which has polymerizable counterions, and 2) permanently fixing the surfactant monolayer on the SWNTs by in situ free radical polymerization of the counterions, followed by ultracentrifugation and freeze drying. SANS measurement of the p-SWNTs in $D_2O$ indicates that isolated SWNTs are cylindrically encapsulated by polymerized surfactant monolayers. It is remarkable that the p-SWNTs are still readily re-dispersible in water, even after harsh processing such as freeze drying, indicating their excellent stability and processibility. Therefore, the p-SWNTs provide us an unique opportunity to explore the rich phase behavior of polymeric systems as templates to fabricate various self-organized SWNT superstructures. The first polymeric system used to fabricate self-assembled SWNT superstructure is the P84/water/p-xylene ternary system which shows a lamellar and a reverse hexagonal phase at room temperature when the composition in weight ratio is 40/40/20 and 46/18/36, respectively. The contrast varied SANS study of the mixtures of p-SWNTs and the P84/water/p-xylene ternary systems indicates that p-SWNTs are preferentially confined to the polar domains of the ternary systems due to the hydrophilically modified surfaces of p-SWNTs. The ...