FTIR and conductivity studies of PVC based polymer electrolyte systems

Poly (vinylchloride) (PVC)-LiBF₄ polymer electrolytes plasticized with DBP in different mole ratios have been studied by FTIR and Impedance Spectroscopic techniques. The complexation has been confirmed from FTIR studies. The maximum room temperature conductivity (2.1·.10⁻⁷ S·.cm⁻¹) has been observed for PVC-LiBF₄-DBP (10-5-85 mole%) complex. The temperature dependence of the conductivity of the polymer films seems to obey the VTF relation. The conductivity values are presented and the results are discussed.     

Some EPR spin probe and spin label studies of polymer systems

The application of EPR spin probe and spin label technique for solving the two problems of polymer physical chemistry is considered. The first problem is the determination of conformational state and chain sizes in amorphous solid polymers. This determination is based on the analysis of the intramolecular dipolar broadening of EPR spectra of spin labelled macromolecules in glassy solvents or in the bulk of unlabeled polymers at 77 K. The second problem is the determination of molecular mobility and structure of two polymer colloid systems: (a) the complex of colloidal silica and synthetic polycation macromolecule and (b) polymer-surfactant micellar organized systme.     

Impedance and dielectric studies of nanocomposite polymer electrolyte systems using MMT and ferroelectric fillers

Impedance and dielectric properties of nanocomposite polymer electrolyte systems modified with nano size MMT and ferroelectric fillers have been investigated for varying lithium to oxygen ratios. The changes in the structural properties of the electrolyte samples were characterized by X-ray diffraction (XRD) and differential scanning calorimetric (DSC) technique. The ion transport number estimated by DC polarization technique is found to be between 0.86 and 0.95. The bulk conductivities of nanocomposite polymer electrolyte films were studied using impedance spectroscopic technique. The impedance plot shows high frequency semicircle, due to the bulk effect of sample and maximum ionic conductivity of 2.15 × 10⁻⁴ Scm⁻¹ was observed for (PEO)₄LiCBSM at 323 K with lithium to oxygen ratio 1: 4. The complex impedance data was used to evaluate ionic conductivity and dielectric relaxation process, to understand the ion transport mechanism in these systems.

     

Impedance spectroscopy studies of poly (methyl methacrylate)-lithium salts polymer electrolyte systems

In the present work, five systems of samples have been prepared by the solution casting technique. These are the plasticized poly(methyl methacrylate) (PMMA-EC) system, the LiCF₃SO₃ salted-poly(methyl methacrylate) (PMMA-LiCF₃SO₃) system, the LiBF₄ salted-poly(methyl methacrylate) (PMMA-LiBF₄) system, the LiCF₃SO₃ salted-poly(methyl methacrylate) containing a fixed amount of plasticizer ([PMMA-EC]-LiCF₃SO₃) system, and the LiBF₄ salted-poly(methyl methacrylate) containing a fixed amount of plasticizer ([PMMA-EC]-LiBF₄) system. The conductivities of the films from each system are characterized by impedance spectroscopy. The room temperature conductivity in the pure PMMA sample and (PMMA-EC) system is 8.57 × 10⁻¹³ and 2.71 × 10⁻¹¹ S cm⁻¹, respectively. The room conductivity for the highest conducting sample in the (PMMA-LiCF₃SO₃), (PMMA-LiBF₄), ([PMMA-EC]-LiCF₃SO₃), and ([PMMA-EC]-LiBF₄) systems is 3.97 × 10⁻⁶, 3.66 × 10⁻⁷, 3.40 × 10⁻⁵, and 4.07 × 10⁻⁷ S cm⁻¹, respectively. The increase in conductivity is due to the increase in number of mobile ions, and decrease in conductivity is attributed to ion association. The increase and decrease in the number of ions can be implied from the dielectric constant, ɛ_r-frequency plots. The conductivity–temperature studies are carried out in the temperature range between 303 and 373 K. The results show that the conductivity is increased when the temperature is increased and obeys Arrhenius rule. The plots of loss tangent against temperature at a fixed frequency have showed a peak at 333 K for the ([PMMA-EC]-LiBF₄) system and a peak at 363 K for the ([PMM-EC]-LiCF₃SO₃) system. This peak could be attributed to β-relaxation, as the measurements were not carried out up to glass transition temperature, T _g. It may be inferred that the plasticizer EC has dissociated more LiCF₃SO₃ than LiBF₄ and shifted the loss tangent peak to a higher temperature. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7–9, 2006     

Transport studies on filler-doped chitosan based polymer electrolyte

The room temperature conductivity of the chitosan complex containing 40 wt.% of salt increased from 6.02×10⁻⁶ Scm⁻¹ to 2.10×10⁻⁵ Scm⁻¹ after the addition of 1.0 wt.% aluminosilicate. Conductivity of the electrolyte is contributed from the charge carrier density and ionic mobility. The Rice and Roth model was applied in calculating the mobility, μ and density of ions, n. The number density of ions, n, increases with temperature, while mobility, μ decreases with increasing temperature. This work also suggests that the filler did not change the conduction mechanism of the charge carrier in chitosan-salt-filler complexes but helped to increase the conductivity value of the materials. Paper presented at the International Conference on Functional Materials and Devices 2005, Kuala Lumpur, Malaysia, June 6 – 8, 2005.     

Impedance of nonuniform distributed solid protonic electrolyte - polymer systems

The conductivity of mixtures of the solid electrolytes H₃[PMo₁₂O₄₀]·13H₂O and Cs₂H[PW₁₂O₄₀] · 13H₂O follows the predictions of the percolation theory, whereas the electrode impedance in the high frequency range fits well the model of double layer adsorption relaxation. It is concluded that both the adsorption relaxation and the reversibility of the electrodes are related to oxygen transfer, the oxygen ions being the minority charge carriers. Fast oxygen dispersion may occur at the polymer-solid electrolyte interface. Paper presented at the 2nd Euroconference on Solid State Ionics, Funchal, Madeira, Portugal, Sept. 10–16, 1995     

Electrical and structural studies of a LiBOB-based gel polymer electrolyte

A series of gel polymer electrolytes (GPEs) containing lithium bis(oxalato)borate (LiBOB), propylene carbonate (PC), and ethylene carbonate (EC) have been investigated. Poly(ethylene oxide) (PEO) was used as the polymer. First, a series of liquid electrolytes was prepared by varying the Li:O ratio and obtained the best composition giving the highest conductivity of 7.1?×?10^?3 S cm^?1 at room temperature. Then, the PEO-based GPEs were prepared by adding different amounts of LiBOB and PEO into a mixture of equal weights of EC and PC (40 % of each from the total weight). The gel electrolyte comprises of 12.5 % of LiBOB, 7.5 % of PEO, 40 % of EC, and 40 % of PC gave the highest ionic conductivity of 5.8?×?10^?3 S cm^?1 at room temperature. From the DC polarization measurements, ionic nature of the gel electrolyte was confirmed. Fourier transform infrared (FTIR) spectra of electrolytes showed the Li⁺ ion coordination with EC and PC molecules. These interactions were exhibited in the peaks corresponding to ring breathing of EC at 893 cm^?1 and ring bending of EC and symmetric ring deformation of PC at 712 and 716 cm^?1 respectively. The presence of free Li⁺ ions and ion aggregates is evident in the peaks due to the symmetric stretching of O–B–O at 985 cm^?1.     

Dielectric and conduction mechanism studies of PVA-orthophosphoric acid polymer electrolyte

Polyvinyl alcohol (PVA)-based proton conducting polymer electrolytes have been prepared by the solution cast technique. The conductivity is observed to increase from 10⁻⁹ to 10⁻⁴ S cm⁻¹ as a result of orthophosphoric acid (H₃PO₄) addition. The plot of conductivity vs temperature shows that a phase transition occurred at 343 K in the sample PVA-33 wt% H₃PO₄. The β-relaxation peak is observed at 313 K. The glass transition temperature of PVA-33 wt% H₃PO₄ is 343 K. Orthophosphoric acid seems to play a dual role, i.e., as a proton source and as a plasticizer. The ac conductivity σ _ac = Aω ^s was also calculated in the temperature range from 303 to 353 K. The conduction mechanism was inferred by plotting the graph of s vs T from which the conduction mechanism for sample PVA-17 wt% H₃PO₄ was inferred to occur by way of the overlapping large polaron tunneling (OLPT) model and the conduction mechanism for the sample PVA-33 wt% H₃PO₄ by way of the correlated barrier height (CBH) model.     

Conductivity studies of plasticized anhydrous PEO-KOH alkaline solid polymer electrolyte

Polyethylene oxide (PEO)–potassium hydroxide (KOH)-based alkaline solid polymer electrolyte films have been prepared by using methanol as solvent. The highest room temperature ionic conductivity of (2.1 ± 0.5) × 10⁻⁸ S cm⁻¹ was achieved for the composition of 70 wt% PEO:30 wt% KOH. The addition of plasticizer, ethylene carbonate, propylene carbonate, or polyethylene glycol to the highest conductivity of PEO–KOH system helps to increase the ambient ionic conductivity to the order of 10⁻⁶–10⁻⁴ S cm⁻¹. The log σ vs 1/T plot of PEO–KOH showed a small conductivity decrease at 50–60 °C range. The small decrease and the hysteresis that occur during the heating–cooling cycle was overcome by the presence of the plasticizer. X-ray diffraction observation supports the conductivity results.     

Effect of gamma irradiation on the polymer electrolyte PEO-NH4ClO4

Irradiation affects the structures of materials at different scales, thus changing physical and chemical properties. We study here the effect of gamma irradiation at different doses on the polymer electrolyte PEO-NH₄ClO₄. Optical micrographs show cracks in the irradiated samples and impedance spectroscopy measurements indicate reduced ion-conductivity at room temperature but slight enhancement at higher temperature. At high frequencies, the real part of the admittance shows a power-law variation; the exponent, which is a measure of self-similarity of the structure, is reduced on irradiation. The overall results point to a more disordered structure at higher radiation doses.     

The effects of ceramic fillers on the PMMA-based polymer electrolyte systems

The effects of ceramics fillers on the polymethylmethacrylate (PMMA)-based solid polymer electrolytes have been studied using ac impedance spectroscopy and infrared spectroscopy. The polymer film samples were prepared using solution cast technique, tetrahydrofuran (THF) used as a solvent, and ethylene carbonate (EC) has been used as plasticizer. Lithium triflate salt (LiCF₃SO₃) has been incorporated into the polymer electrolyte systems. Two types of ceramic fillers, i.e., SiO₂ and Al₂O₃, were then implemented into the polymer electrolyte systems. The solutions were stirred for several hours before it is poured into petri dishes for drying under ambient air. After the film has formed, it was transferred into desiccator for further drying before the test. From the observation done by impedance spectroscopy, the room temperature conductivity for the highest conducting film from the (PMMA–EC–LiCF₃SO₃) system is 1.36 × 10⁻⁵ S cm⁻¹. On addition of the SiO₂ filler and Al₂O₃ filler, the conductivity are expected to increase in the order of ∼10⁻⁴ S cm⁻¹. Infrared spectroscopy indicates complexation between the polymer and the plasticizer, the polymer and the salts, the plasticizer and the salts, and the polymer and the fillers. The interactions have been observed in the C=O band, C–O–C band, and the O–CH₃ band. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7-9, 2006.     

Effect of PVAc dispersal into PVA-NH4SCN polymer electrolyte

The present paper deals with ion transport studies on a new proton conducting composite polymer electrolyte — (PVA_x:NH₄SCN)_y:PVAc system. Complexation and morphology of the composite electrolyte films are discussed on the basis of X-ray diffraction and differential scanning calorimetry data. Coulometry and transient ionic current measurements revealed charge transport through protons. The maximum ion conductivity was found to be 7.4·10⁻⁴ S·cm⁻¹ for the composition: x=0.15, y=0.12. The observed conductivity behaviour is correlated to the morphology of the films. The temperature dependence of the electrical conductivity exhibits Arrhenius characteristics in two different temperature ranges separated by a plateau region related to morphological changes occurring in the electrolyte.     

Polyvinyl pyrrolidone/Mg(ClO4)2 solid polymer electrolyte: structural and electrical studies

Polymer electrolytes comprising polyvinyl pyrrolidone (PVP) as host polymer and Mg(ClO₄)₂ as dopant salt have been prepared by solution casting technique using double-distilled water as solvent. The changes in the structural properties on the incorporation of dopant were investigated by XRD and FTIR analysis. The ionic conductivity and dielectric behavior were explored using AC impedance spectroscopy. The ionic conductivity increases with increasing dopant concentration. The conductivity enhancement with the increasing salt concentration is correlated with the increase in amorphous nature of the electrolytes. The frequency dependence of electrical conductivity obeys the universal Jonscher power law. The electrical modulus representation shows a loss feature in the imaginary component. The distribution of relaxation times was indicated by a deformed arc form of the Argand plot. The relative dielectric constant (ε _r ) decreases with increase in frequency in the low frequency region whereas a frequency-independent behavior is observed in the high frequency region. The total ionic transference number studies have confirmed that the mobile charge carriers are ions. Results obtained by cyclic voltammetry on SS/60 mol% PVP/40 mol% Mg(ClO₄)₂ SPE/SS symmetrical cell show evidence for reversibility.

     

AC impedance studies on proton conducting polymer electrolyte complexes (PVA+CH3COONH4)

A proton conducting polymer electrolytes of pure polyvinyl alcohol and polyvinyl alcohol complexed with ammonium acetate having different compositions have been prepared by solution cast technique. FTIR spectrum confirms the complexation process. The conductivity of the pure polyvinyl alcohol is in the order 10⁻¹⁰ S/cm at ambient temperature and its value increases 10⁴ times when complexed with 20% ammonium acetate. The Arrhenius plot for all electrolyte shows two different regions above and below the glass transition temperature. A high dielectric loss value is observed for the case of complexed PVA in comparison to pure PVA. Based on the study of relaxation spectra, it is found that the relaxation time decreases with increase in temperature and dopant concentration. Paper presented at the 2nd International Conference on Ionic Devices, Anna University, Chennai, India, Nov. 28–30, 2003.     

Field enhanced Li ion conduction in nanoferroelectric modified polymer electrolyte systems

Nanocomposite polymer electrolyte (NCPE) films based on polyethylene oxide (PEO) complexed with lithium perchlorate (LiClO₄) and nanosized ferroelectric ceramic fillers such as BaTiO₃, SrTiO3 have been prepared using solution cast technique. The films showed very good mechanical stability when exposed to ambient atmospheres for prolonged periods. Lithium ion transport studies revealed that the conductivity is predominantly ionic. The effect of electric field on ionic conductivity of NCPE films was investigated. One order enhancement in conductivity due to the field was observed at 323 K. NCPE films exhibited conductivity of 3.46?×?10^?5 Scm^?1 at 323 K. NCPE films were characterized using differential scanning calorimetry (DSC) and X-ray diffraction (XRD) technique. The DSC and XRD studies revealed reduced crystallinity which confirmed the higher amorphous phase and hence the improved ionic conductivity.     

Electrical conductivity studies on PVA/PVP-KOH alkaline solid polymer blend electrolyte

A series of conducting thin-film solid electrolytes based on poly (vinyl alcohol)/ poly (vinyl pyrrolidone) (PVA/PVP) polymer blend was prepared by the solution casting technique. PVA and PVP were mixed in various weight percent ratios and dissolved in 20 ml of distilled water. The samples were analyzed by using impedance spectroscopy in the frequency range between 100 Hz and 1 MHz. The PVA/PVP system with a composition of 80% PVA and 20 wt.% PVP exhibits the highest conductivity of (2.2±1.4) × 10⁻⁷ Scm⁻¹. The highest conducting PVA/PVP blend was then further studied by adding different amounts of potassium hydroxide (KOH) ionic dopant. Water has been used as solvent to prepare PVA/PVP-KOH based alkaline solid polymer blend electrolyte films. The conductivity was enhanced to (1.5 ± 1.1) × 10⁻⁴ Scm⁻¹ when 40 wt.% KOH was added. Paper presented at the International Conference on Functional Materials and Devices 2005, Kuala Lumpur, Malaysia, June 6 – 8, 2005.     

Electrochemical cell performance studies on all-solid-state battery using nano-composite polymer electrolyte membrane

All-solid-state proton-conducting polymeric batteries have been fabricated in the cell configurations: Zn + ZnSO₄·7H₂O (anode) || polyethylene oxide (PEO):NH₄HSO₄ + SiO₂ || MnO₂ + C (cathode) and Zn + ZnSO₄·7H₂O (anode) || PEO:NH₄HSO₄ + SiO₂ || PbO₂ + V₂O₅ + C (cathode). Nano-composite proton-conducting polymeric membrane in wt.% composition, 92PEO: 8 NH₄HSO₄ + 3 SiO₂, synthesized by solution cast technique, has been used as electrolyte. Dispersal of nanosized (8 nm) fumed-SiO₂ particles resulted into an enhancement in the room temperature conductivity of polymer electrolyte host, 92PEO: 8 NH₄HSO₄ (wt.%), approximately by an order of magnitude with the substantial increase in the mechanical strength of the films. Details on the electrolyte film casting and ion transport characterization studies have been discussed elsewhere in the literature. However, a brief mention has been made for reference. An open circuit voltage in the range 1.5–1.8 V, obtained for both the batteries, is in very good agreement with the value reported. The cell performance has been studied under varying load conditions. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7–9, 2006.     

Nucleotide Spin Labeling for ESR Spectroscopy of ATP-Binding Proteins

Site-directed spin labeling of proteins by chemical modification of engineered cysteine residues with the molecule MTSSL (1-oxyl-2,2,5,5-tetramethylpyrroline-3-methyl methanethiosulfonate) has been an invaluable tool for conducting double electron electron resonance (DEER) spectroscopy experiments. However, this method is generally limited to recombinant proteins with a limited number of reactive Cys residues that when modified will not impair protein function. Here, we present a method that allows for spin labeling of protein-nucleotide-binding sites by adenosine diphosphate (ADP) modified with a nitroxide moiety on the β-phosphate (ADP-β-S-SL). The synthesis of this ADP analog is straightforward and isolation of pure product is readily achieved on a standard reverse-phase high-performance liquid chromatography (HPLC) system. Furthermore, analyses of isolated ADP-β-S-SL by LC–mass spectrometry confirm that the molecule is very stable under ambient conditions. The crystal structure of ADP-β-S-SL bound to the ATP pocket of the histidine kinase CheA reveals specific targeting of the probe, whose nitroxide moiety is mobile on the protein surface. Continuous wave and pulsed-ESR measurements demonstrate the capability of ADP-β-S-SL to report on active site environment and provide reliable DEER distance constraints.     

Mathematical modeling of field-assisted Li ion conduction in nanocomposite solid polymer electrolyte systems

Ionics - Nanocomposite solid polymer electrolyte films were prepared to study the effect of electric field on the ionic conductivity. The studies were carried out by varying the electric field from...