Radiation and Temperature Effects on Conductivity and Dielectric Properties of Poly (Vinyl Alcohol)-Potassium Hydroxide-Propylene Carbonate

The physical and chemical properties of polymeric materials can be modified by treatment with ionizing radiation. This radiation processing technique has been used to modify the structural and electrical properties of polymer composites for use as electrical devices. Alkaline composite polyrner electrolytes (ACPEs) are materials that have attracted great attention for their vast application in the development of solid-state ionic devices. The materials have their chemical and electrical properties change with radiation dose allowing modification of the electrolytes in the solid state form. One serious problem of the ACPEs is low ionic conductivity at room temperature because they have a tendency to crystallize. In this study radiation-processing technique was chosen to increase the ionic conductivity at room temperature. The ACPE consists of poly(viny1 alcohol) (PVA) as the host polymer, potassium hydroxide (KOH) as an ionic blend and propylene carbonate (PC) as a plastisizer. The compositions of KOH and PC were varied from 40 to 70%. The electrolytes were prepared by chemical method and the finished films were obtained by solvent-casting technique. The films were irradiated with 1.25 MeV gamma rays with dose from 0 to 200 kGy at room temperature. The sample of irradiated and unirradiated films of different compositions was placed between two parallel-plate metal electrodes and the conductivity and dielectric properties were measured using an impedance analyzer at different frequencies ranging from 20 Hz to 1 MHz. For the unirradiated samples, the conductivity and dielectric properties were also measured at different temperatures of narrow range from room temperature to 343 K. The X-ray diffraction (XRD) measurements were performed to characterize the change of molecular structure of the electrolytes with radiation dose and compositions of the blend and plastisizer. The results show that the ACPE sample of PVA-KOH (40 wt.%)- PC (60 wt.%) irradiated with dose 200 kGy exhibits the highest ionic conductivity of 2.7 x 10'~s cm-' at room temperature. For ACPE sample with PVA-KOH (40 wt.%)-PC (60 wt.%) the highest ionic conductivity value is 7.8 x scm-' at 343 K. The results show that the frequency dependent conductivity and dielectric constant of the ACPEs depend on radiation dose, temperature and composition of the blends and plastisizer. From the XRD analysis, the molecular structure of the electrolytes change from semi-crystalline to amorphous when the composition of PC increased to 60% and the radiation dose increased to 200 kGy. Finally, we have demonstrated that radiation processing can be used to modify ACPEs to increase their ionic conductivity for the development of solidstate ionic devices.

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