Characterization of double walled carbon nanotubes-polyvinylidene fluoride nanocomposites

One of the main objectives of this thesis is to disperse double-walled carbon nanotubes (DWNT) in a polyvinylidene fluoride (PVDF) matrix, and to characterize the resulting composite using electrical, thermal, and mechanical characterization techniques. DWNTs are successfully dispersed in the PVDF, and this dispersion is assessed by using optical microscopy and both scanning and transmission electron microscopy. The second objective of this study is to investigate the morphology of the PVDF after adding the carbon nanotubes. The results using the x-ray diffraction technique do not show change in the PVDF morphology with addition of DWNTs. In Differential scanning calorimetry study the results show that the melting temperature does not vary much with addition of DWNTs. An increase in the crystallization temperature and a decrease in the percent crystallinity is also observed as DWNT content increases. The electrical and mechanical properties of the composites are measured and data is used to calculate the percolation volume fraction using electrical conductivity. The results show that the percolation threshold occurs at 0.23 vol%, which is a low volume fraction further indicating a good dispersion. The critical exponent implies a three dimensional dispersion. The predicted volume fraction at percolation using the excluded volume approach indicates that the DWNTs are dispersed in small bundles of seven hexagonally closed packed tubes. The mechanical properties are done using dynamic mechanical analysis to study the effect of the nanotubes on the mechanical properties. The results show that the storage modulus is enhanced 84% by adding 4.51 vol% DWNT-PVDF below the glass transition temperature which is in a -45????C region and it is increased by about 97% at 40????C. Electromechanical performance of the composites is assessed by testing the actuation behavior using DC voltage. The results show no actuation for volume contents below percolation, and a measurable actuation at volume contents above percolation. Results from the different characterization techniques indicate that the DWNTs are successfully dispersed. An enhancement in electrical conductivity and dielectric constant is achieved by addition of DWNTs. At DWNT volume content above percolation, both mechanical and electromechanical enhancements are observed, as evidenced by DMA and electroactive characterization techniques.