It is very important to find out how gamma irradiation affects the crystallinity of PS to investigate the structural modification of lattice properties of the crystals Fig. 7. (a) shows the XRD patterns of PS loaded with a 10% concentration of Al2O3 nanoparticles and irradiated with varying gamma doses. As seen in Fig.
7. (a). The PS crystallinity is reduced with an increasing gamma-absorbed dose. The gamma irradiation served to enhance the interaction between the organic moiety and the inorganic network. This reaction increases the covalent bonding between the Al2O3 nanoparticles and the PS matrices, which causes further branching and destroys crystallinity.
This is indicative of the evolution of a disordered state in the polymer and hence amorphization. The crosslinking between the filler surface and the polymer led to the formation of smaller crystallites, which in turn act to prevent ordering locally. Fig.
7. (c). shows the calculated crystallite size as a function of the gamma-absorbed dose.
It can be observed that the crystal size increases with an increasing gamma-absorbed dose. This may be attributed to the occurrence of cross-linking in the polymer chain, meaning that the cross-linking of the polymer molecules resulted in a significant increase in molecular mass. This in turn will increase the number of polymer chains surrounding the nanoparticle. Fig. 7.
(d). Shows that both the interplanar spacing (d) and interchain separation (R) increase with an increasing gamma-absorbed dose as gamma irradiation leads to a noticeable separation between the polymer chains. This result may reflect the fact that the polymer matrix suffered from some kind of structural rearrangement due to the irradiation treatments.UV Visible studies Fig.
8. (a). Shows the effect of gamma irradiation on the UV vis of PS loaded with a 10% concentration of Al2O3 nanoparticles that was irradiated at different gamma irradiation doses. A shift in the absorption edge towards the visible region (larger wavelength) was observed after irradiation, which indicates a decrease in the band gap after irradiation. The progressive shift of the absorption edge as a result of irradiation, inferred by the rupturing of bonds resulting in cross-linking, led to the formation of new bonds. This result confirms the modification of the chemical structure, the production of defects, and disordering induced by irradiation.
This is in a good agreement with the results obtained by XRD. On the other hand, we can observe from Fig. 8. (b). That the transmittance of nanocomposites decreased with the increase of gamma dose for all values of the wavelength due to the fact that the interaction of gamma radiation induces defects during its passage through the samples which lead to a modification in the order at the structure of the samples. These samples possess fine uniform grains with no big pores which lower the transmittance and increase absorbance.
Optical band gap and activation energyFig. 9. Shows the obtained energy gap as a function of the gamma-absorbed dose. It can be clearly seen that the energy gap decreases with an increasing dose. This indicates that the gamma irradiation influences the crosslinking of the nanocomposite. This cross-linking is caused by the formation of new covalent bonds and therefore new chains were obtained, while the motion of molecules was hindered and their activity was reduced, consequently decreasing the optical band gap. In other words, the irradiation causes cross-linking that reduces crystallinity and induces lattice defects.
The lattice defects may act as scattering centers and energy barriers, which increase the electronic disorder and reduce the optical band gap. Fig shows the optical activation energy (EU) as a function of the gamma irradiation absorbed. The activation energy is shown to have increased with an increasing electron irradiation dose for all irradiated samples. This may be due to the enhancement of the disorder in the PS polymer resulting in a decrease in the band gap after irradiation. This produced defects in the polymers, which increased the amount of disorder leading to the occurrence of structural deformation phenomena in the polymer.
Refractive index and dielectric propertiesThe refractive index of the PS loaded with a 10% concentration of Al2O3 nanoparticles that was irradiated at different gamma doses were calculated and plotted as a function of the wave length shown in Fig. 10. (a). As can be seen, the refractive index increased slightly with an increasing gamma dose. This indicates that the gamma irradiation led to the predominance of the cross-linking process, allowing for the formation of covalent bonds between different chains. This in turn minimized the anisotropic character of the nanocomposite samples, leading to an increase in the refractive index. Moreover, the gamma irradiation enhanced the spreading of Al2O3 inside the PS matrix.
This assisted in the formation of intermolecular hydrogen bonding between Al2O3 with the adjacent OH group of PS, and in turn minimized the anisotropic character of the nanocomposite samples. Figs. 10 (b), (c) show the variation in real part and imaginary part of dielectric constant respectively of the PS loaded with a 10% concentration of Al2O3 nanoparticles, irradiated with different gamma doses. It can be seen that the real and imaginary part increased with increasing gamma absorbed. This is associated with increasing refractive index and absorption coefficients after irradiation.Optical conductivityAs shown in Fig 11, the optical conductivity increases with increasing gamma radiation dose.
This could be attributed to enhancement in the amorphous nature of the samples after irradiation. Also, this increasing behavior of the optical conductivity value is associated with increase in the values of both n and k at any given wavelength.
