Influence of aspect ratio of carbon nanotubes on crystalline phases and dielectric properties of poly(vinylidene fluoride)

Poly(vinylidene fluoride) (PVDF)-multiwalled carbon nanotube (MWNT) composites with different aspect ratios of MWNT were prepared by a Coagulation method. Field emission scanning electron and transmission electron microscopic studies reveal that MWNT are well dispersed in the PVDF matrix. The X-ray diffraction and differential scanning calorimeter data indicate that the composites with high aspect ratio of MWNT have the beta phase structure at the MWNT loading level of 2.0wt%, and have a mixture of alpha and beta phase below 2wt% MWNT, and that those composites with low aspect ratio of MWNT, however, always have a mixture of alpha and beta phase for MWNT concentrations <= 2.0wt%. The dielectric constant values increase with the increase in MWNT loading level and the percent increase in dielectric constant is much greater in the composite filled with high aspect ratio of MWNT than in that loaded with low aspect ratio. And also, it has been found that the dielectric loss of the composites with MWNT loading level <= 2.0wt% is still as low as neat PVDF, which is of significance for dielectric application. (C) 2008 Elsevier Ltd. All rights reserved.