Glass Transition and Relaxation Processes of Nanocomposite Polymer Electrolytes (original) (raw)
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The frequency dependent dielectric and conductivity behavior of a plasticized polymer nanocomposite electrolytes (PPNCEs) based on poly(ethylene oxide) + NaClO 4 with dodecyl amine modified montmorillonite (DMMT) as the filler and poly(ethylene glycol) as the plasticizer have been studied. The formation of nanocomposites and changes in the structural and microstructural properties of the materials were investigated by x-ray diffraction (XRD) and optical microscopy techniques. Studies of dielectric properties at lower frequencies show that the relaxation contribution is superimposed by electrode polarization effect. The appearance of peak for each concentration in the loss tangent suggests the presence of relaxing dipoles in the polymer nanocomposite electrolyte (PNCE) films. On addition of plasticizer, the peak shifts towards higher frequency side suggesting the speed up the relaxation time. The variation of ac conductivity with frequency obeys Jonscher power law except a small deviation in the low frequency region due to electrode polarization effect. The dc conductivity increases with increase in plasticizer concentration. Analysis of frequency dependence of dielectric and modulus formalism suggests that the ionic and polymer segmental motions are strongly coupled.
Relation between structural and conductivity relaxation in PEO and PEO based electrolytes
Solid State Ionics, 2014
The effect of a lithium salt on the general polymer dynamics of poly(ethylene oxide) (PEO) and how these dynamical alterations affect the ionic conductivity and structural relaxations in (PEO) 4 :LiClO 4 have been investigated. The study was based on differential scanning calorimetry (DSC) and dielectric relaxation studies. The DSC studies indicated an increased glass transition temperature of (PEO) 4 :LiClO 4 as compared to that of PEO. The polymer-salt complex exhibited enhanced conductivity of σ D.C. = 3.2 × 10 −7 S·cm −1 at room temperature (298 K) due to the presence of mobile Li + ions. Impedance data have been scaled and analyzed under conductivity and modulus formalisms over wide ranges of frequency and temperature for both PEO and (PEO) 4 :LiClO 4 . For PEO, the analysis of the scaled formalisms indicates that both the conductivity and the structural relaxation mechanisms are temperature-independent above the melting point of PEO. However, below the melting point, the nucleation and growth of spherulites and also the formation of 'interphase' regions in PEO result in a hindered long range D.C. conductivity, which, in turn, leads to a decoupling of the D.C. conductivity and the structural relaxation. However, for (PEO) 4 :LiClO 4 , by comparing the conductivity relaxation data with the calorimetric glass transition and analysis of scaled formalisms, a direct coupling between Li + ion motions and polymer segmental dynamics is observed for the polymer electrolyte.
Current Applied Physics, 2012
Frequency and temperature dependences of dielectric permittivity and electric modulus of pure and Ba-doped Bi 2 Ti 4 O 11 were studied in the ranges of 10 Ϫ1 -10 6 Hz and Ϫ150-350°C, respectively. We found that the antiferroelectric phase transition temperature of Bi 2 Ti 4 O 11 decreases with Ba doping. In the permittivity studies, we also observed dielectric relaxation peaks shift to higher temperature with increasing frequency. Furthermore, in the electric modulus formalism, conducting peaks were uncovered above 150°C in addition to the dielectric relaxation peak. We discussed the mechanisms for the dielectric relaxation and conduction processes based on TiO 6 octahedra distortion and a space-charge model.
The Journal of Physical Chemistry B, 2004
The conductivity and transport properties of a composite polymer electrolyte were studied by comparing the structure and dynamics as a function of both salt and organic-inorganic composite content. The system consisted of poly(ethylene oxide) (PEO), an organic-inorganic composite (OIC) prepared from aluminum tri-sec-butoxide and [(3-glycidyloxy)propyl]trimethoxysilane (GLYMO) and lithium triflate (LiCF 3 SO 3). The systems with and without salt yielded strikingly different physical properties when the OIC content exceeded 50%. Through analysis of 29 Si NMR spectra, it was found that the lithium ion of LiCF 3 SO 3 (LiTf) promotes the condensation of GLYMO, which peaks near 50% OIC content. Also, short-range structural evidence for PEO-OIC blending at high OIC content was observed in the salt-free system through comparisons of the line shapes of the 27 Al NMR spectra. This blending is absent in the ternary system due to prominent PEO-LiTf interactions, as confirmed by X-ray, DSC, and impedance spectroscopy experiments. Furthermore, the glass transition temperature exhibits a linear increase as a function of OIC content, whereas the conductivity over this range first shows a sharp increase followed by a mild decrease. The dielectric constant also was found to vary nonlinearly with OIC content, indicating that ionic screening is modulated by OIC. Because in this system the conductivity and the glass transition temperature do not show a significant correlation, although structurally it is clear that PEO and salt are intimately mixed, a model was developed for the transport that focuses principally on the density of mobile lithium ions. The model predicts relatively constant ion mobilities and diffusion constants but a strongly varying mobile ion number density as a function of OIC content, which then explains the dependence of conductivity on OIC content in this electrolyte.
Characterisation of PEO–Al 2 O 3 composite polymer electrolytes
The behaviour of PEO 8 LiClO 4 with different quantities of a-Al 2 O 3 or g-Al 2 O 3 was investigated using DSC, AC conductivity and 7 Li NMR experiments. DSC results showed that the presence of the filler does not change the glass transition temperature of the electrolyte but, on the other hand, modifies the quantity of its crystalline phase. From the AC impedance measurements, it was observed that the sample with the highest conductivity at room temperature is PEO 8 LiClO 4 5.3 wt.% a-Al 2 O 3 . The change in the quantity of crystalline phase cannot alone explain the conductivity data, and it is suggested that the space charge contribution in the interphase of the filler particles and the polymeric chains influences the behaviour of the samples. The 7 Li NMR results showed that line width narrowing begins at temperatures close to T g . From the hydrogen decoupling experiments it was possible to estimate the Li H average distances as 2.7 A , . The Li Li distance was calculated as being between 2.6 and 3.5 A , depending on the number of near neighbours lithium nuclei used in the model.
Concentration dependence of ionic relaxation in lithium doped polymer electrolytes
Journal of Non-Crystalline Solids, 2010
This is an author produced version of a paper published in Journal of Non-Crystalline Solids. This paper has been peer-reviewed but does not include the final publisher proof-corrections or journal pagination. Citation for the published paper: Furlani, M. et. al. "Concentration dependence of ionic relaxation in lithium doped polymer electrolytes"
Influence of crystallization on dielectric properties of PEO:LiTFSI polymer electrolyte
Journal of Non-Crystalline Solids, 2006
Impedance spectra of the PEO 8 :LiN(CF 3 SO 2 ) 2 electrolyte were measured in the frequency range from 0.01 Hz to 10 MHz at temperatures between À65°C and 90°C in various heating and cooling runs. Polarizing microscope observations confirmed that a rapidly cooled electrolyte remained amorphous below À15°C. Crystallization during slow cooling took place at +15°C. Presence of the crystalline phase caused significant reduction of the strength of b relaxation and to a lesser degree the strength of a relaxation. The a relaxation time in the amorphous phase of semicrystalline electrolyte is considerably shorter than that in the entirely amorphous sample. Ionic conductivity fell more than 10 times during crystallization. Conductivity of the semicrystalline electrolyte decreased upon cooling much slower than in the case of the amorphous electrolyte. At temperature about À35°C conductivity became equal in both states of the electrolyte. The temperature dependence of conductivity and frequency of a relaxation indicated that the glass transition in the semicrystalline electrolyte occurred at a temperature about 10°C lower than in the amorphous sample. This finding was confirmed by the results of DSC study. Lower glass transition temperature of the amorphous regions is a consequence of depletion of the salt, which is accumulated in the lamellae of the PEO 6 :LiN(CF 3 SO 2 ) 2 crystalline complex.
Journal of Polymer Science Part B: Polymer Physics, 2011
Polymer electrolytes, (PEO:LiClO 4 )þx IL (1-Buty-3methylimidazolium hexafluorophosphate) with varying concentration of IL; x ¼ 0,5,10,15,20 wt % have been prepared by solution cast technique and characterized by X-Ray diffraction, differential scanning calorimetery, FTIR, conductivity and dielectric relaxation measurements in the frequency range of 100 Hz-5 MHz. Temperature dependence of relaxation frequency and conductivity were found to be typical of thermally activated process both at T > T m and T < T m . Composition dependence of conductivity, dielectric relaxation, and degree of crystallinity has also been studied. On addition of IL, the degree of crystallinity after a decrease at 5 wt % IL increases slightly at 10 wt % and then finally decreasing. Variation of conductivity and relaxation frequency with composition could only be partly explained on the basis of variation of degree of crystallinity. An additional feature of ion-ion interaction (contact ion pair formation between IL or salt cations and their associated anions) has been invoked which was supported by FTIR studies.
Dielectric relaxation and thermal studies on dispersed phase polymer nanocomposite films
Journal of Materials Science: Materials in Electronics, 2014
Dispersed phase polymer nanocomposite films (PNC) based on PMMA-LiClO 4 ? n-YSZ, has been prepared. The effect of filler concentration on dielectric constant, tand and ac conductivity has been observed. For each PNC films the activation energy for relaxation (E s ) is almost same as the activation energy for ion conduction (E a ). The dc conductivity, the hopping frequency of charge carriers have been obtained at different temperature from the analysis of the ac conductivity data. For all the PNC films, the concentration of charge carriers has been calculated at different temperature using Almond-West formalism. The estimated activation energies for the dc conductivity and the hopping frequency are different, which indicates that the both charge carrier mobility and concentration contribute significantly to the ionic conductivity of polymeric electrolyte. Contribution of charge carrier mobility to the total conductivity has also been confirmed from the differential scanning calorimetry analysis. Improvement in thermal stability has been noticed with filler addition.
Dielectric and conductivity relaxations in PVAc based polymer electrolytes
Ionics, 2004
The polymer electrolytes composed of a blend of poly (vinyl acetate) (PVAc) and poly (methylmethacrylate) (PMMA) as a host polymer and LiClO4 as a salt are prepared by a solution casting technique. The formation of blend polymer- salt complex has been confirmed by FT-IR spectral studies. The conductivity- temperature plots are found to follow an Arrhenius nature. Arrhenius plot shows the decrease in activation energy with the increase in salt concentration. The dielectric behaviour of the sample is analysed using dielectric permittivity (ε′), dielectric loss (ε″) and electric modulus (M″) of the samples. The impedance cole- cole plot shows the high frequency semi- circle is due to the bulk effect of the material and the depression in the semicircle shows the non-Debye nature of the material. The bulk conductivity is found to vary between 2.5×10−5 Scm−1 to 1.7×10−3 Scm−1 with the increase of salt concentration of blend polymer samples. The migration energy derived from the dissipation factor is almost equal to the activation energy calculated from conductivity. The modulus spectrum of the samples shows the non-Debye behaviour of the polymer electrolyte films. The low frequency dispersion of the dielectric constant implies the space charge effects arising from the electrodes.