الفهرس 
Theoretical Background and Literature ReviewOnly 14 pages are availabe for public view
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Abstract
Over the past few decades, solid polymer electrolytes have received considerable attention due to their potential applications in solid state electrochemical devices like rechargeable batteries, super capacitors, fuel cells and chemical sensors. The present study is concerned with the effect of addition of LiClO4 on the structural, thermal, electrical and optical properties of PVC-co-PVAc / LiClO4 polymer electrolytes. The positron annihilation spectroscopy has been applied to investigate microstructural properties of the studied composites. The results of PAL and DBAR are employed to investigate the effect of addition LiClO4 on the free volume holes in PVC-co-PVAc / LiClO4 SPE system and discussed in relation to the observed changes in ionic conductivity, dielectric parameters and optical properties.
The results obtained may be summarized as follows:
The variations in τ3 and I3(%) as a function of LiClO4 concentration gives information about the manner at which the dopant affects the free volume hole size and concentration. Doping the polymer matrix with (Li+) and (ClO4−) ions occupy the free volume of smaller size present in the composite at initial doping level and hence reflects the constant at initial doping stage. At higher doping level, Li+ ions or molecules occupy the bigger size of free volumes. Therefore, the availability of free volumes in the composite reduces which reflects a DROP in τ3 values from 2.027 to 1.8366 ns. A steep decrease in the calculated values of the free volume size (Vf) with increasing doping concentration reflects the DROP in τ3 and I3(%).
The profile of the halos in the XRD patterns refers to the dominant amorphous phase and the addition of LiClO4 salt, causes the amorphous halo to be more broaden (W increase). FTIR spectra revealed the coordination of both ClO4− and Li+ ions with the carbonyl carbon and carbonyl oxygen, respectively. The pure PVC-co-PVAc polymer has a glass transition temperature Tg of 76.5 C and increased to 95.2 C at 20 wt % LiClO4. The shift of Tg to higher temperature is due to the interaction of Li-ions with electron-rich coordinating groups, such as ether and carbonyl group, via transient crosslinking bonds. These bonds obstruct the rotation of the polymer segments and hence increase the energy barrier to the segmental movement.
The dc ionic conductivity increases from 2x10-10 S/m for the neat host material (PVC-co-PVAc) to over 5.5x10-7 S/m for 30 wt.% LiClO4 doped sample. The percolation threshold is observed for 20 wt.% LiClO4. The values of Ea is decreased with increasing LiClO4 content, which implies a diverse conduction mechanism rather than the ion random walking through the amorphous polymer electrolyte. Miyamoto -Shibayama model was to correlate the free volume and ionic electrical conductivity dc, with a value of critical free volume Vi* for the charge carriers/ions transport in PVC-co-PVAc / LiClO4 polymer composites equal to 90.9 (Å3).
The dielectric constant ε’ increases with increasing LiClO4 content up to 20 wt(%) for all frequencies due to the increased dipole polarizations. A frequency dependent behavior of the ac conductivity has appeared in the high frequency region, where its value increased rapidly with frequency due to the increase in the number of free charge carriers that are trapped and confined to potential wells. The size of free volume holes for PVC-co-PVAc)/LiClO4 SPE is negatively correlated with both permittivity έ and dielectric loss ε’’ that is the polarity of LiClO4 being higher than that of the host copolymer itself which leads to an increase in electrical parameters and to an inhibition of o-Ps formation.
The optical properties of PVC-co-PVAc / LiClO4 SPE films are studied in the wavelength range (200-1400 nm). The reduction in the transmission of the samples by increasing LiClO4 content leads to a decrease in due the structural changes of the polymer. The refractive index (n) increases with increasing LiClO4 content which can be illustrated by the increase of the sample density by doping LiClO4 salt in the main chain of the polymer as well as the complexation in the SPE. The Doppler broadening S parameter is linearly proportional to the direct and indirect optical energy band gap. Such proportional originates from the increase in o-Ps annihilation in vacancies or free volume cavities with minimal momentum electrons of the atoms present at vacancies or cavities walls in non-crystalline domains of the polymer. The refractive index n is inversely proportional to the free volume hole size which indicates that n is highly dependent on the internal structure of the polymer material, such as molecular weight, defect distributions, crosslinking and free volume size and concentration.