Papers by Author: Ri Hanum Yahaya Subban

Abstract: Poly(vinyl) chloride (PVC)-NH₄I-EC films have been prepared by solution cast technique. The sample containing 30 wt. % NH₄I exhibited highest room temperature conductivity of 4.60 × 10^-7 S cm^-1. The conductivity increased to 1.08 × 10^-6 Scm^-1 when 15 wt. % of ethylene carbonate (EC) was added to 70 wt. % PVC - 30 wt. % NH₄I. Fourier Transform Infrared (FTIR) showed evidence of polymer–salt complexation while DSC showed increase in glass transition temperature (T_g ) of PVC -NH₄I - EC polymer electrolytes. The conductivity behavior of the studied system could be accounted by the changes in T_g values.

Abstract: Free standing polymer electrolyte films comprising of ammonium trifluoromethane sulfonate in poly(ethyl methacrylate) were prepared and characterized. The structural and electrical properties of the polymer electrolytes were investigated by X-ray diffraction and a.c. impedance spectroscopy, respectively. The formation of polymer-salt complex has been confirmed by Fourier transform infrared spectroscopy study. Conductivity of the polymer electrolytes increased with salt content. The highest ionic conductivity in the order of 10-5 S cm-1 at room temperature was achieved for the system with 35 wt% of ammonium salt. The temperature dependence of conductivity obeyed the Vogel-Tammam-Fulcher relation. The activation energy has been calculated from the VTF formalism. The ionic transference number of the mobile ions estimated by Wagner’s polarization method was close to unity for the highest conducting sample implying that the conductivity was contributed by ions which was expected to be protons.

Abstract: (100-x) LiClO_4-xSiO₂ (x is mol %) solid composite electrolytes in various compositions were synthesized by modified sol-gel process with sintering at 200 °C. The electrical and structural properties of the composites were investigated. The ionic conductivity of the composites increased with mol % of the dispersoid and then decreased. The highest conductivity was obtained for x = 50 mol % with a value of 4.06 × 10^-7 S cm^-1 at room temperature. The enhancement in conductivity was more than two orders of magnitude when compared to the host material. The higher conductivity in the SiO₂ dispersed system was interpreted in terms of space charge layer and percolation theory. The temperature dependence of conductivity of all samples were Arrhenian in nature and exhibited a maximum of 10^-3 S cm^-1 at T = 140 °C for x = 50 mol %. XRD spectra showed presence of heterogeneous phase of LiClO₄-SiO₂ crystalline peaks.

Abstract: Hexanoyl chitosan: LiClO₄: TiO₂ composite electrolyte films were prepared by the solution cast technique. The ac conductivity and dielectric properties of the samples prepared have been studied in the frequency range from 100 Hz to 1 MHz over the temperature range from 273 to 333 K. The exponent s in the Jonscher’s universal power law, σ(ω)=σ_dc+Aω^s was analyzed as a function of temperature and the analysis suggests that the conduction mechanism can be interpreted based on the correlated barrier hopping (CBH) model. The barrier heights, W_M were calculated. The values of W_M are found to decrease with increasing temperature in the same manner as the exponent s. Both dielectric constant and dielectric loss decrease with increase in frequency and increase with increase in temperature.

Abstract: Solid polymer electrolytes comprising of various weight ratios of poly(ethyl methacrylate) (PEMA) and lithium perchlorate (LiClO4) salt were prepared via solution casting technique using N,N-Dimethylformamide (DMF) as the solvent. The conductivity values of the electrolytes were determined utilizing Solatron 1260. The highest conductivity obtained is in the order of 10-6 S cm-1. Structural properties of the electrolytes were investigated by X-ray diffraction and the results show that the highest conducting film is the most amorphous.