Optical Study of Pva Based Gel

Bulletin of Materials Science, 2004

An attempt has been made in the present work to prepare polyvinyl alcohol (PVA) based proton conducting gel electrolytes in ammonium thiocyanate (NH 4 SCN) solution and characterize them. DSC studies affirm the formation of gels along with the presence of partial complexes. The cole-cole plots exhibit maximum ionic conductivity (2⋅ ⋅58 × 10 -3 S cm -1 ) for gel samples containing 6 wt% of PVA. The conductivity of gel electrolytes exhibit liquid like nature at low polymer concentrations while the behaviour is seen to be affected by the formation of PVA-NH 4 SCN complexes upon increase in polymer content beyond 5 wt%. Temperature dependence of ionic conductivity exhibits VTF behaviour.

Macromolecules, 1993

The gelation mechanism of poly(viny1 alcohol) (PVA) aqueous solutions in the presence of vanadate ions was studied from the rheological and spectroscopic points of view. A phase diagram of PVA and vanadate ions was constructed as a function of PVA and sodium vanadate concentrations as well as pH. It was found that PVA aqueous solutions became a gel in the presence of H2VloOze4-vanadate ions, which are exclusively formed in the pH range 2-3. Furthermore, ultraviolet (UV) absorption spectra of these solutions indicate that only H2V100284-ions among more than 10 kinds of vanadate ions were responsible for the complex formation with PVA molecules. This observation was in good agreement with the phase behavior. The viscosity of PVA solutions containing vanadate ions was measured for several PVA concentrations below and above the so-called C* concentration, i.e., the chain overlap concentration. The viscosity increased with time when C was larger than C*. On the other hand, the viscosity decreased for C < C*. The time evolution of the viscosity and UV spectra was also studied. It was found that PVA solutions having only H2VloO28'ions had a significant time dependence in the viscosity and UV absorption behavior. These facta were successfully explained by the concepta of inter-and intra-cross-linking formations and time-dependent hydrogen-bonding formation.

International Journal of Polymeric Materials, 2007

The structural, electrical, and optical characteristics of nanometric Fe 2 O 3−x films fabricated on ͗100͘ Si and SiO 2 substrates by ablating an iron target with a KrF excimer laser in low pressure ͑0.05-1.0 Pa͒ O 2 atmosphere are reported. The thickness of films fabricated with 4000 laser pulses is ϳ80 nm for samples deposited at the lowest pressure ͑0.05 Pa͒ and decreases gradually to 50 nm at the highest used pressure ͑1.0 Pa͒. The film mean composition results close to FeO at lower pressures ͑0.05-0.10 Pa͒ and to Fe 2 O 3 at higher pressures ͑0.5-1.0 Pa͒. From glazing incidence x-ray diffraction spectra, it was inferred that deposits are poorly crystallized, especially the ones prepared at relatively high oxygen pressures ͑0.5-1.0 Pa͒. Scanning electron microscopy inspections show that surfaces are plane and uniform, with very rare ͑Ͻ0.1 m −2 ͒ submicron droplets. From x-ray reflectivity spectra, surface roughness results very low ͑0.1-0.5 nm, increasing with O 2 pressure͒. The films present a semiconductor behavior, with electrical energy gaps increasing from 0.43 to 0.93 eV with increasing O 2 pressure, while the optical energy gap varies from 1.60 eV ͑0.05 Pa͒ to 1.74 eV ͑1.0 Pa͒. Very high thermoelectromotive force coefficient values were measured ͑up to 1.65 mV/K͒. It is also shown that films present promising gas sensing properties.

PVA has been doped by different percentage of Lithium Iodide (LiI), electrical and optical properties of polymer electrolytes have been investigated. At low frequency, the variation of dielectric constant and dielectric loss with frequency shows the presence of material electrode inter-face polarization processes. The exponent factor found is between 0.98 and 0.442 and obeys the universal power law. The absorption of pure and doped films have been studied in the visible and ultra-violet wavelength regions. It has been observed that the new absorption peaks at 290 and 375 nm are due to the formation of charge transfer complex. From direct allowed transition the optical energy gap decreases from 5.56 eV (for pure PVA) to 4.95 eV (for PVA+20%LiI).

Molecules

Presently, the rising concerns about the fossil fuel crisis and ecological deterioration have greatly affected the world economy and hence have attracted attention to the utilization of renewable energies. Among the renewable energy being developed, supercapacitors hold great promise in broad applications such as electric vehicles. Presently, the main challenge facing supercapacitors is the amount of energy stored. This, however, does not satisfy the increasing demand for higher energy storage devices, and therefore, intensive research is being undertaken to overcome the challenges of low energy density. The purpose of this review is to report on solid polymer electrolytes (SPEs) based on polyvinyl alcohol (PVA). The review discussed the PVA as a host polymer in SPEs followed by a discussion on the influence of conducting salts. The formation of SPEs as well as the ion transport mechanism in PVA SPEs were discussed. The application and development of PVA-based polymer electrolytes o...

An attempt has been made in the present work to combine gel and composite polymer electrolyte routes together to form a composite polymeric gel electrolyte that is expected to possess high ionic conductivity with good mechanical integrity. Polyethylene glycol (PEG) based composite gel electrolytes using polyvinyl alcohol (PVA) as guest polymer have been synthesized with 1 molar solution of ammonium thiocyanate (NH4SCN) in dimethyl sulphoxide (DMSO) and electrically characterized. The ionic conductivity measurements indicate that PEG : PVA : NH4SCN-based composite gel electrolytes are superior (σmax = 5.7 × 10 −2 S cm −1 ) to pristine electrolytes (PEG : NH4SCN system) and conductivity variation with filler concentration remains within an order of magnitude. The observed conductivity maxima have been correlated to PEG : PVA : NH4SCNand PVA : NH4SCN-type complexes. Temperature dependence of conductivity profiles exhibits Arrhenius behaviour in low temperature regime followed by VTF character at higher temperature.

Indonesian Journal of Fundamental and Applied Chemistry

Research on the effect of electrolyte ammonium salt, concentration electrolyte with plasticizer to ionic and electronic conductivity of polymer gel electrolyte has been conducted with the variations of two electrolyte NH 4 Cl-PVA and NH 4 SCN-PVA at a concentration of 10, 30, 40 (wt%). The measurement of using ionic conductivity by using impedance spectroscopy method showed that the highest value was 0.0156 Scm-1 i.e. in the 54.6% propilen carbonate with 40% NH 4 Cl and PVA. The lowest value was 0.009 Scm-1 i.e. in the NH 4 SCN based electrolyte without propilene carbonate and electronic conductivity showed that the highest value was 0.0156 Scm-1 i.e. 40% NH 4 Cl-PVA and NH 4 SCN-PVA and the lowest value was 0.009 Scm-1 , i.e. in the NH 4 SCN based electrolyte without propilene carbonate. Factorial analyses showed that the concentrations of electrolyte and the plasticizer affect conductivity value. FTIR (Fourier Transform Infrared) measurement showed that the addition of propilene carbonate did not show new bond formation between electrolyte and PVA. It can be shown in absence of characteristic wave number for propilene carbonate and NH 4 + ion.

Electrochimica Acta, 1995

electrolytes based on polymethymetacrylate (PMMA) have been obtained using propylene carbonate and ethylene carbonate as gelating agents. They have a good mechanical stability, solvent retention and high electrical conductivity at room temperature (about 10e3 Sem-'). In the aim of understanding the possible interactions of the mobile ions with polymer or solvent molecules, a comparative Raman study has been carried out on samples containing all the components of the gel electrolytes or some of them. The interaction with Li+ ions induces appreciable modifications of the vibrational spectra of the solvent molecules; two new bands appear at 9OOcm-' and 730cm-', slightly upshifted with respect to the stretching and bending modes of the ethylene carbonate ring. The change in size and polarizability of the anion species does not affect such cation-solvent interaction.

The structural and ion transport studies of PVAx:NH4SCN solid polymer electrolytes (SPEs) with the aim of developing suitable ion conducting electrolytes for solid state ionic devices have been reported. DSC, XRD and IR analysis of as synthesized films have been carried out to study morphology and complexation behavior of PVA with NH4SCN. A possible structure of PVA complex has been proposed on the basis of IR spectroscopy. The electrical characterization which comprises of I - t, coulometery, TIC measurements and impedance spectroscopy has been carried out to assess ion transport behaviour of these complexes. The electrical measurement evidenced cationic transport with maximum in electrical conductivity of 7.0x10-5 S cm-1 for x = 0.15 in the system. The compositional variation of ionic conductivity has been correlated to morphology and concentration of charge carriers.

European Scientific Journal, 2014

Solid polymer electrolyte films based on polyvinyl alcohol complexed with Barium nitrate salt at different weight percent were prepared using solution cast technique. The optical absorption coefficient was used to study the nature of electronic transitions between the valence and conduction bands. From the derivation of Tauc's relation it was found that the optical absorption is due to directand indirect allowed transitions. The reduction of energy band gap and increase of tail localized states was observed with increasing Barium nitrate content. The values of refractive index, extinction coefficient, the optical complex dielectric constant have been also calculated. The higher refractive index of solid polymer electrolytes was attributed to the higher molecular packing density compared to that of pure polymer. The increase of optical dielectric constant with increasing salt concentration indicates the presence of a higher density of states and increase in the amount of charge carrier concentration within the polymer electrolyte films.

SN Applied Sciences, 2021

The significant breakthroughs of flexible gel electrolytes have attracted extensive attention in modern wearable electronic gadgets. The lack of all-around high-performing gels limits the advantages of such devices for practical applications. To this end, developing a multi-functional gel architecture with superior ionic conductivity while enjoying good mechanical flexibility is a bottleneck to overcome. Herein, an architecturally engineered gel, based on PVA and H3PO4 with different molecular weights of PVA for various PVA/H3PO4 ratios, was developed. The results show the dependence of ionic conductivity on molecular weight and also charge carrier concentration. Consequently, fine-tuning of PVA-based gels through a simple yet systematic and well-regulated strategy to achieve highly ion-conducting gels, with the highest ionic conductivity of 14.75 ± 1.39 mS cm-1 have been made to fulfill the requirement of flexible devices. More importantly, gel electrolytes possess good mechanical ...

2013

Polymer blends of poly (vinyl alcohol) (PVA) and PEDOT:PSS (poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate)), were prepared by casting from aqueous solution. They were characterized by x-ray diffraction, scanning electron microscopy, differential scanning calorimetery, thermo gravimetric analysis, Fourier transform infrared, ac spectroscopy and optical UV-visible absorption techniques. The thermal analysis did not illustrate significant variations of PVA when blended with different concentrations of PEDOT:PSS. The bulk conductivity of PVA/PEDOT:PSS blend illustrated a two orders increase, while the activation energy reduced from 0.52 to 0.16 eV with an increasing PEDOT:PSS concentration to 4 wt%. In addition, the frequency dependence of conductivity obeyed the power relation σ ∼ ω s , 0.3 < s < 0.45, which predicts ionic diffusion. The dielectric constantέ and dielectric loss ε obeyed, at ambient temperature, the Debye dispersion relations in a wide range of frequencies. A new significant optical broad absorption peak appeared in the visible range around 926 nm. Its height increased by increasing the PEDOT:PSS concentration, which was attributed to a direct energy band gap, in the range 1.05-1.2 eV, and plasmon-exciton interaction.

The solution cast technique was used to prepare composite films of polyvinyl alcohol with different Kaolin light concentrations. The optical absorption measurements were carried out for all samples at room temperature across the (190 -1100 nm) wavelength regions. The optical parameters including the energy band gaps and band tail width for the samples are investigated; it was found that the optical absorption is due to direct transition, and the optical energy gaps values shifted to lower energies on kaolin light concentration from 5.53 eV for pure PVA to 5 eV for 20% kaolin addition, whereas the magnitudes of the Urbach energy tends to increase with increasing kaolin light concentration from 0.69 eV for pure PVA to 2.51 eV for 20% kaolin addition. In general the kaolin content in polymer matrix caused an increase of extinction coefficient values, which is a result of increasing the number of atomic refractions due to the increase of the linear polarizability. Thermal study of the composite films was investigated. From thermogravimetric analysis it was found that the thermal stability of the PVA sample is decreased with increasing kaolin content.

The effect of silver nanoparticles doped in PVA on the structural and optical properties of composite films is studied experimentally. Samples are PVA films of 0.14 mm thickness doped with different sizes and concentrations of silver nanoparticles. Structural properties are studied using X-ray diffraction and FTIR spectrum. Using the reflectance and transmittance of samples, the effect of doped nanoparticles and their concentration on optical parameters of PVA films include absorption coefficient, optical bandgap energy, complex refractive index, complex dielectric function, complex optical conductivity, and relaxation time is extracted and discussed. The dispersion of the refractive index of films in terms of the single oscillator Wemple-DiDomenico (WD) model is investigated and the dispersion parameters are calculated. Results show that by doping silver nanoparticles in PVA, number of Bragg's planes in the structure of polymer and its crystallinity are increased noticeably. Ag-O bonds are formed in the films and the bandgap energy of samples is decreased. Calculations based on WD model confirm that by doping nanoparticles, the anion strength of PVA as a dielectric medium is decreased.

2009

The electrical conducting mechanism of newly synthesized polymer by condensation polymerization, poly vinyl alcohol grafted with Eosin dye (PVA-g-Ei ) have been investigated. Electrical measurements including (current-voltage) and (conductivity-Temperature) characteristics at a range of temperature ( 313- 368)K.The result shows that the sample has semiconductor behavior as its conductivity increases with the increasing temperature and the value of dark conductivity at R.T estimated from Ohmic region was about 1.04x10 -13 S/cm .The energy required to move electrons from valance band to conduction band can be estimated which about 0.52eV.The deviation from Ohmic law has been analyzed in terms of variable range hopping (VRH) conduction theories. Thermal properties were also studied to estimate the bipolar contribution to thermal conductivity of polymer.