الفهرس 
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Abstract
Polymer composites are intensively studied for the new properties which are given by the combination of the properties of both polymer matrix and the filler respectively. When the concentrationof the filler in the composite reaches the percolation value, the continuousbulk network structure is formed. If electrical conductive filler (Carbon black (CB)) is used, the composite properties can change from insulator to conductive ones.Electrical conductivity can change in the magnitude of several orders. Radar absorbing materials (RAMs) are the various processed materials whose function is to attenuate the electromagnetic radiation in the microwave band and may be obtained as: paints, composites, sheets, thin films, etc.Such materials are obtained from the addition of determined absorbing fillerinto different types of polymeric material. The combination of polymers with carbon nanotubes allowslinking the properties of both materials to form new functional materials, with application in the microwave area. In recent years, polymer nanocomposites and understanding their physical and chemical properties have attracted great attention. The presence of nano-particles in polymerimproves the mechanical, electrical and optical properties of the materials; metal oxide nano-particles doped polymers have been studied as alternative materials for optical applications such as planner waveguide devices and micro-opticalelements.Many polymers have been proved to be suitable materials in the development of composite structuresdue to their ease of production and processing good adhesion with reinforcing elements, resistanceto orrosive environment, light weight, and in some casesductile mechanical performance. Polymerwaveguides have been fabricated by CO2 laser ablation, which is a pure photo-thermal effect, occurring at an energy density above a threshold. There is however, no detailed report of any optical property modifications of polymer induced by CO2 laser Radiation at an energy density below the ablation threshold. Sampleswere prepared in three steps. First, the solution samples were prepared by dissolving 1wt% SDS in distilled water using magnetic stirrer (corning hot plate stirrer PC-351) at 250C for 1 hr. In the second tep different weights of MWCNTin volume fraction(0.004, 0.009, 0.019, 0.029 and 0.038) were dispersed in the SDS/H2O solutions by using a high power ultrasonic homogenizerat room temperature for 20min. Finally solutions were prepared by dissolving 8wt %of PVA in sonicated solutions by using a magnetic stirrer at 800C for 2hr from the filler content (Carbon nanotube) dependence of the electrical (DC) conductivity of PVA composites wenotice that in the case of very low filler concentration, the composites conductivity remains almost the same of that of the polymeric matrix. If the filler loading exceeds a certain critical value, however, a drastic rises in the composites conductivity by several orders of magnitude can occur. The dielectric constant of PVA/CNT nano-filler composites dependence on frequency, έ decreases as frequency increases showing usual dispersion.At low frequencies, the polarization follows the change of the electric field. In this case, highest value of έis obtained. At high frequencies, the electric field changes too fast for polarization effects to appear The dependence of AC conductivity of PVA/ carbon nanotubecomposites as a function of volume fraction of carbon nanotubecontent showed that the AC conductivity increased with increasingthevolume fraction of carbon nanotubeaccording to classical percolation theory.As obtained from the data of shield effectiveness due to absorption, and the total shield effectiveness due reflection and SEL ( the correction term induced by the reflecting waves inside the shielding barrier), the total shield effectiveness increased by increasing the volume fraction and frequency and the SEAcomprise a major portion of the EMI SE. The maximum value (89.9dB) of SETis obtained at (35GHz) for the composites with V ≥ (0.029).In case of loaded PVA with carbon nano-filler contents less than the percolation threshold, one could observe a gradual decrease in σacwith laser energy up to 100 Joules followed by an abrupt increase till 150 Joules. This may be attributed to the increase of the amount of accumulated charge (due to laser beam) which causes increase in the polarization effects. PVA loaded with higher concentration of carbon nanotube (0.019<0.029) show an exponential decrease in its σac with laser beam energy (up to 200Joules) Meanwhile, PVA samples loaded with 0.038CNT shows an appreciably independent behaviour of its σac with laser energy, which reflects the important role of carbon nanotube in the σac dependent of laser energy. For laser beam energies less than 150 Joules, conductivity of the composites initially increase slowly with increasing the filler (CNT) concentration less than (0.019), followed by a sharp increase in conductivity when the concentration is increased above (0.019) However, the increase of conductivity is marginal when the concentration of(CNT) is increased beyond (0.019) for all laser beam dose ≤ 100 Joules. Increasing the laser beam energies ≥ 150 Joules, one could observe a broadening in the percolation threshold. The skin depth decreases with the increasing contents of CNT by approximately 400 times its initial value by loading the matrix by (0.038) of CNT. Meanwhile, this ratio of decreasing is rise to be 4 orders of magnitude after exposing the samples to accumulated laser beam of 200J. The maximum value (129.5 dB) of the SET is obtained at (36.5GHz) for the composites with V= (0.038) after exposed to (200J) laser beam.