الفهرس 
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Abstract
Conclusions
1. MWCNTs, pure PVF and MWCNTs \PVF foam were successfully prepared
with different amounts of MWCNTs with mass ratios of 0 wt %,1 wt %,2 wt
% and 4wt %.
2. We investigate the success of purification process from HRTEM, SEM and
Raman spectra. HRTEM for the purified MWCNTs showed that, MWCNTs
contain 6 walls at least. SEM images for purified MWCNTs showed that
MWCNTs didn’t contain any significant amount of amorphous carbon and
also no evidence of the catalyst existence was seen. SEM images for purified
MWCNTs showed that MWCNTs were prepared with diameters ranging
from 10 to 20 nm, a length of 10 μm at least. The Raman spectra indicate the
formation of MWCNTs with high purity, the ratio D/G = 0.65 for MWCNTs
after the purification.
3. The average pore sizes of pure PVF foam and MWCNTs\PVF foam with
different mass ratios of 1wt%, 2wt% and 4wt% based on SEM images
were100 μm ,77 μm , 71 μm , and 48.8μm , respectively. The open-cell
structure and macroscopically rough surface were observed.
4. FTIR and Raman spectra confirmed the success of the crosslinking process. It
was found that with addition of MWCNTs to PVF, the FTIR characteristic
absorption band for pure PVF (3420 cm-1) shifted to slightly lower values of
wavenumber accompanied with an increase of their intensity. Therefore, the
shift of lower wavenumber may be due to open π- bonds of CNTs and
interactions between CNTs and PVF foam. FTIR showed that there were no
new bands due to the incorporation of little amount of CNTs in PVF foam.
Raman spectra showed that the intensity ratio (D/G) = 0.65 for the purified
MWCNTs and (D/G) = 1 for MWCNTs \ PVF foam. The increase of the
D/G ratio indicated the formation of more defects on the surface of
MWCNTs after the incorporation of the carbon nanotubes in the PVA matrix
foam.
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5. The dielectric permittivity ɛ`, the dielectric modulus M`, M`` and ac
conductivity ζac, for PVF/MWCNTs foam at T= -50oC, 0oC, 100oC and
150oC, were studied. We showed that ɛ` decreased with the increase of
frequencies. This decrease may be attributed to the decrease of the number of
dipoles. On the other hand ε` increased with the increase of the amount of
MWCNTs which could be attributed to interfacial polarization and the
existence of multiple crosslinking configurations in the PVF with MWCNTs.
It was clear that the values of M` increase with frequency and exhibit an S
shaped. This S shaped dispersion of M` is typical of ionic materials also
shifted to higher frequency by MWCNTs content.
6. The near zero values of M` at low frequency indicated the removal of the
electrode polarization for the investigated samples. The frequency
dependency of M``, at various concentration showed that, at low frequency
αa-relaxation peak which is related to the micro-Brownian motion in the
amorphous region of the main polymer chain and shifted to higher frequency
with increasing MWCNTs content. Also, another peak is observed at 1wt%
content of MWCNTs at T= 100oC and 150oC. This peak which occurred at
higher frequency could be ascribed to αc-relaxation. It was associated with
the molecular motions in the crystalline region of the main polymer chain.
αc-relaxation peak is clearly enhanced and slightly shifted toward higher
frequency with increasing MWCNTs.
7. The frequency dependence of ζac within the experimental frequency range
(0.1- 7 MHz), were studied. The results yielded straight lines with different
slopes. The values of s were less than unity i.e., 0<s<1 and decreased with
increasing temperature for all samples. This means that the values of s were
in accordance with the theory of hopping conduction mechanism.