Dose-dependent structural and dielectric response of γ-irradiated PVA/GO/FeGaInS4 nanocomposite films.

Abstract

Poly(vinyl alcohol) (PVA) films containing two dissimilar fillers, graphene oxide (GO) nanosheets and layered FeGaInS4 semiconductor crystallites, were prepared by solution casting and irradiated with 60Co γ-rays at 250, 500 and 1500 kGy. Since the dielectric response of dual-filler composites is governed largely by the polymer-filler interphases, the study aimed to establish how γ-irradiation modifies their polarization and charge transport and which radiation-induced processes are responsible. The films were characterized by X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, electron paramagnetic resonance (EPR) and dielectric spectroscopy. Williamson-Hall analysis indicated that the FeGaInS4 crystallite size remained unchanged within experimental uncertainty at 250 kGy and decreased to about 47 nm at 500 and 1500 kGy, while broadening of the PVA (101) reflection at 1500 kGy revealed a loss of crystalline order in the matrix. EPR revealed radiation-induced radicals, whose concentration was highest at 250 kGy, together with a broad Fe-related resonance that was not affected by irradiation; during 90 days of storage, the radical signal decayed fastest at 250 kGy and most slowly at 1500 kGy, indicating the presence of comparatively stable trapped centers at the highest dose. FTIR spectra indicated dose-dependent modification of intermolecular interactions and chemical bonding in the polymer matrix. The permittivity, dielectric loss, displacement current and ac conductivity decreased at 250 and 500 kGy and increased at 1500 kGy. The frequency exponent s rose from 0.75 to 0.84 and fell to 0.66 at 1500 kGy, while the barrier height W M changed from 1.10 to 1.47 eV and then to 0.94 eV, consistent with correlated barrier hopping in a crosslinked network and an increasing contribution of defect-assisted transport at the highest dose. In contrast to the GO-free FeGaInS4/PVA system, in which irradiation at 500 kGy enhanced the permittivity and conductivity, the GO-containing composite showed the opposite trend, suggesting that the GO-containing interphases promote crosslinking at moderate doses. Moderate γ-doses therefore favor a crosslinked network, whereas high doses lead to degradation and defect-mediated conduction.

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