Non-covalent Modification Of Carbon Nano-materials And Their Applications

In this study, a non-covalent functionalization strategy has been employed tomodify the surface of single walled carbon nanotube (SWNT) and graphene (GR). Inso doing, the vinylimidazole (VI) based polymers (VI-polymers) well known withbiological and/or chemical activities were designed, synthesized, and applied asdispersing agents to perform the surface modification. Besides improving of thedispersibilities of such carbon nanomaterials, it is also desired to endow them withsome new performances such as biocompatibility and chemical sensitivity. After thesuccessful surface modification, the promising applications of surface modifiedSWNTs and GR were explored in the fields of biology and chemical sensors.Four water-soluble VI-polymers bearing different pendant groups weresynthesized by means of free-radical polymerization and chemical complexing andthen tested for preparation of aqueous dispersions of pristine SWNTs. The dispersingefficiency was studied as functions of molecular structure and solution nature ofVI-polymer. The experimental data clearly suggested that charged VI-polymer showshigher dispersing efficiency than its uncharged parent polymer. For a specificVI-polymer, the dispersed SWNT content can be significantly improved by takingsome measures to eliminate/reduce the polymer micelles in the aqueous solution.Under the optimal conditions, the stable aqueous dispersion of SWNTs can reach up to148.9mg·L-1while initial amount of VI-polymer is merely0.06mg·ml-1(~6×10-3wt%), which is far below the amount of sodium dodecyl sulfate (SDS), one of the mostcommonly used dispersant for SWNTs. After being modified, intrinsic electronicproperties of SWNTs were basically preserved. Biocompatibility ofVI-polymer/SWNT complexes obtained from pertinent aqueous dispersion wasassessed by culturing L929cells (mouse fibroblasts). The experimental data indicatethat the complex material is non-toxic to the cells under consideration.Taking VI-polymers as dispersant, a so-called “dispersant-assist liquid-phaseexfoliation method” has been developed to fabricate GR from the starting material ofnatural graphite. Besides the successful acquirement of GR, this method also realizesnon-covalent surface modification of GR. The measurements of UV-vis spectroscopy, atomic force microscopy, and Raman spectroscopy suggest that the dispersant-assistliquid-phase exfoliation method is successful in large-scale preparation of high-qualitygraphene in an economical way. Subsequently, the obtained aqueous GR dispersionwas used as raw material to fabricate a transparent, flexible, and conductive GRmulti-functional film that is supported on a polyester (PET) sheet by a vacuumfiltration followed by a hot-pressing transfer process. When the thickness of GR-layeris65nm, the optical transmittance of GR-PET film in the visible wavelength regionreaches more than50%. When the thickness of GR-layer is80nm, the sheet resistanceof the GR film is as low as105/sq. Furthermore, the GR-PET film shows goodtoughness and excellent bending resistance. More important, the dispersant ofVI-polymer also endows GR-PET film with some new performances, such as chemicalsensitivity. While exposed to the saturated vapor of water, ethanol, acetone, and ethylacetate, the sheet resistance of GR-PET film rapidly changes with the ΔR/R0value of59.1,18.7,17.5, and28.4%, respectively. All the results presented here stronglyindicate that the non-covalent surface modified GR can be promisingly used for thepreparation of chemical sensors.