الفهرس 
Chapter 1 : introduction and literature surveyOnly 14 pages are availabe for public view
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Abstract
The present work is focused on characterization of polymer nano-composite based on polyvinyl alcohol filled with silver nanoparticles or lead sulphide nanoparticles using different techniques. Studied samples have been prepared by wet chemical precipitation technique via casting method. In case of PVA filled with (Ag-nanoparticles), Metal–polymer nano-composites have been prepared from an aqueous solution of polyvinyl alcohol (PVA) and silver nitrate (AgNO3). XRD and SEM measurements revealed that Ag particles are in nanometer size domain. The UV/Vis. spectrum confirmed the formation of Ag-nanoparticles with a surface plasmon band between 420 nm and 478 nm. This result clearly indicates that Ag-nanoparticles are embedded in PVA matrix, and the band gap energies (Eg) obtained decrease with increasing Ag-nanoparticles content. This may indicate that there are charge transfer complexes arose between the PVA and Ag-nanoparticles. DSC revealed that a shift in the melting temperature Tm towards lower temperature regions as Ag-nanoparticles content increases. PVA/Ag-nanoparticles composites have higher conductivity compared with pristine PVA, and it increases as Ag-nanoparticles weight percent increases. The inclusion of metal nanoparticles decreases the interfacial barrier and increases the transition probability of electron hopping across the barrier and insulator chains, which in turn provides a conducting path through the amorphous regions of the polymer matrix resulting in enhanced conductivity. XRD scans revealed the semicrystalline nature of the PVA polymer and showed an increase of Ag-nanoparticles crystallinity at expense of PVA matrix, and also reveals that silver metal is present in face centered cubic (FCC) crystal structure. For PVA films filled with PbS-nanoparticles, The UV/Vis. spectrum confirmed the formation of PbS-nanoparticles with a high absorption intensity peak and an optical band gap higher than the bulk PbS due to quantum confinement in PbS nanocrystallites. XRD scans revealed the semicrystalline nature of the PVA polymer and also revealed that PbS-nanoparticles are present in FCC crystal structure. DSC revealed that the increase in the PbS-nanoparticles content decreases the melting temperature, increases the glass transition temperature and degradation temperature of the PVA matrix, and also revealed that the degradation mechanism of the nanocomposite differs from that of pure PVA. TEM micrographs show that spherical nanoparticles are formed with particle size near 20 nm. DC conductivity of the samples depends on the PbS ions concentration and temperature change.