Modification of Carbon Nanotubes Using Poly(vinylidene fluoride) with Assistance of Supercritical Carbon Dioxide: The Impact of Solvent

We report herein a typical piezoelectric polymer, poly(vinylidene fluoride) (PVDF) to be successfully wrapped on single-walled carbon nanotubes (SWCNTs) using a simple supercritical carbon dioxide (SC CO2) antisolvent-induced polymer epitaxy method. Our study focused on the effect of different solvents on the morphology of PVDF wrapping on SWCNTs. Three organic solvents, dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMAc) were chosen for PVDF. When DMSO was used as solvent, the decorating degree of PVDF on the surface of SWCNTs increases significantly with the increase of SC CO2 pressure, and nanocrystals wrapping on SWCNTs can be observed at high pressure. FTIR and Raman spectra indicated that there exist interactions between SWCNTs and PVDF chains. What's more, FUR results also show that there exists a transformation from the beta-phase to the alpha-phase of PVDF in DMSO with the assistance of SC CO2, which is similar to the action of elongation/shear flow field. It indicated that the alpha-phase is the predominant form occurring on the surface of SWCNTs after treatment with SC CO2. And the helical structure on SWCNTs observed from the TEM image reflected the alternate trans- and gauche-bond conformation of the alpha-form. When DMF or DMAc was used as the solvent, although nanocrystal wrapping and helical structure was not visible, the samples had more excellent dispersion than that in DMSO. Particularly, for DMF, a typical network structure was observed, which is similar to a spider web. Therefore, this work supplies a clue that the various morphologies of nanohybrid structure can be obtained just by changing the solvent during the treatment process of SC CO2, and accordingly, the tailored nanohybrid structure are promising and important for functional design as a basic component in microfabrication and other fields.