الفهرس 
Chapter 1Only 14 pages are availabe for public view
Abstract
Reduced graphene oxide (RGO) doped polyvinyl alcohol/ polyethylene glycol (PVA/PEG) films were prepared by solution casting technique and exposed to 100 kGy gamma radiation. The structural modifications in the samples before and after irradiation were studied using
X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry DSC. The free volume holes (V_f ) determined from the ortho-positronium (o-Ps) lifetime (τ_3) measured by the positron annihilation lifetime spectroscopy (PALS) is found to decrease from (84.52 to 67.24 Å^3) and from (85.67 to 78.21 Å^3) for nonirradiated and irradiated samples respectively with increasing the nanoscale RGO filler volume fraction in the range from (0 to 0.265) into the polymer matrix. The resulting decrease of the free volume holes size due to this incorporation could be explained by both the formation of hydrogen-bonding and crosslinking between RGO and PVA/PEG blend as confirmed by scanning electron microscope (SEM) images, XRD and FTIR measurements. A decrease is also observed in the concentration of free volumes (F_r) for both nonirradiated and irradiated samples. The increased DC electrical conductivity with increasing RGO volume fraction (0–0.265) suggests a conductivity chain formation through the nanoparticle aggregation. The deduced Ln σ_dc is found to be positively correlated with the probability of free annihilation of positrons (I_2%) with electrons at crystalline-amorphous interfaces. σ_dc results could be successfully fitted using the model suggested by Miyamoto and Shibayama. The critical free volumes for the charge carriers transport has been deduced to be 80.34 and 82.16 Å^3 for nonirradiated and irradiated samples respectively. The dielectric properties have been studied as a function of frequency in the range from (100 Hz to 1 MHz) and temperature in the range from (303 to 373 K). It is found that the dielectric constant (ε’) and dielectric loss (ε″) show a frequency dependence at low frequencies and an independent behaviour at high frequencies. According to the temperature dependence of (ε’), relaxation peaks were observed in all samples and assigned to the micro-Brownian motion of the polymer blend chains. Enhancement of (ε’) and (ε^″ ) with the incorporation of RGO nanofiller, could be explained by Maxwell -Wagner- Sillar effect due to the presence of the interfacial polarization. The conduction mechanism is assigned to the correlated barrier height (CBH) from the dependence of the AC conductivity with frequency. An enhancement in the mechanical properties is observed with the incorporation of RGO till 0.099 volume fraction for nonirradiated and 0.165 for the irradiated samples respectively. This behaviour is in accordance with the Halpin- Tsai model.