J. P. Calame

Electrical relaxation in pure and alkali metal thiocyanate complexed poly(ethylene oxide)

Abstract : Audio frequency complex admittance and DSC studies have been performed on pure poly(ethylene oxide) (PEO) and PEO complexed with alkali metal thiocyanates over the temperature range 5.5-380K. The dielectric constant of the complexed materials is found to be greater than for pure PEO. A discontinuity in the conductivity is found which increases in temperature as the size of the cation increases. In every case, the discontinuity is associated with a feature in the DSC results. Next, some evidence is given that water may enhance the formation of amorphous complexed PEO. In pure PEO, alpha sub a and gamma relaxations are observed in good agreement with previous work. A thermal anomaly is found corresponding to alpha sub a . In addition, alpha sub c is identified in pure PEO. Very little difference is found for the gamma relaxation between pure PEO and PEO-LiSCN and PEO-NaSCN. For PEO-KSCN, three distinct peaks are found in the gamma relaxation region. These results are consistent with a tg+t infinity tg-t transition interpretation for gamma where the cations reside within the helical channels at low temperatures. (Author)

Effect of Pressure on Conductivity in Poly(Ethylene Oxide) Complexed with Alkali Metal Salts.

Abstract Audio frequency complex admittance measurements at a number of temperatures have been performed on PEO complexed with various alkali metal perchlorates and thiocyanates at pressures up to 0.3 GPa. In general, the activation volumes tend to increase with the size of both the cation and anion. The trend is best explained if the ion transport mechanism involves both anions and cations. The results are in good agreement with the predictions of a dynamical diffusion theory with an attempt mode Gruneisen parameter appropriate for interchain vibrations. This implies that diffusion takes place via interstice-interstice hopping of the ions. Next, it is shown that free volume considerations lead to unreasonable results if T o is interpreted as the glass transition temperature. Finally, the effect of pressure on the activation volume is determined.

Thermally stimulated depolarization current studies of poly(ethylene oxide) and poly(ethylene oxide) complexed with potassium thiocyanate

A digitally controlled thermally stimulated depolarization current facility is described and measurements on poly(ethylene oxide) (PEO) and PEO complexed with potassium thiocyanate (KSCN) are reported. The results complement and extend previous electrical relaxation studies on these materials. In particular, in PEO the presence of a relaxation previously labeled αc is confirmed. The relaxation is assigned to defects in the crystalline phase. In addition, the γ relaxation region is shown to consist of at least two relaxations. Further, a high‐temperature family of peaks is obtained which are associated with space charge. For KSCN‐complexed PEO three low‐temperature relaxations are observed in the γ relaxation region. The relationship between these relaxations and previously reported dielectric relaxation results is established and possible origins of the relaxations are discussed. Finally, differential scanning calorimetry studies were carried out on all of the materials.

DSC and high pressure conductivity and electrical relaxation measurements in PPO and PPO complexed with lithium salts

Abstract Differential scanning calorimetry and high pressure electrical conductivity studies have been carried out on poly(propylene oxide) after the addition of various lithium salts. In addition, high pressure electrical relaxation measurements have been performed in the glass transition region on uncomplexed PPO. The vacuum conductivity measurements show that T 0 is 30–40°C lower than the DSC Tg. Next, it is found that both T 0 and Tg increase several K/kbar. In terms of the configurational entropy model, the isobaric data yield a reasonable value for the activation volume which is consistent with values previously reported for PEO complexed with alkali metal ions. The isothermal data yield a negative activation volume for PPO complexed with LiSCN. Finally, DSC and isothermal conductivity measurements show that neither T g nor the apparent activation volume scale directly with ion size.

Dielectric relaxation in poly(ethylene oxide) complexed with alkali metal perchlorates

Abstract Audio frequency complex admittance measurements over the temperature range 5.5–350 K have been performed on poly(ethylene oxide) (PEO) complexed with lithium and sodium perchlorates. No evidence of an αa relaxation was seen in any sample. In the Li-complexed material, the γ relaxation occurs at about 174 K and 1000 Hz which is the same as for pure PEO. In the Na-complexed materials, there appear to be more than one peak in this region, and the relative peak heights are concentration dependent. The result is that at the 8:1 doping level, there is a broad, skewed relaxation whose peak occurs at about 203 K and 1000 Hz, while at 4.5:1 NaClO4 the relaxation appears much closer to a normal peak with a maximum at 185 K for the 1000 Hz data. Combined with previous results for thiocyanate complexed PEO, these results show that distortions in the polymer chain depend on both the cation and anion. Next, two new relaxations are observed at low temperatures. The first, occuring at 60–100 K is very weak and is common to all PEO samples. The second occuring at very low temperatures, is only found for perchlorate complexed PEO and is attributed to the localized motion of perchlorate-induced defects on the exterior of the chains. The high temperature electrical conductivity for PEO8:NaClO4 is found to be larger than PEO4.5:NaClO4 in agreement with the trend observed by other workers for PEO complexed with different alkali metal salts.

Conductivity, DSC, FTIR, and NMR studies of poly(vinyl acetate) complexed with Alkali metal salts

Abstract Electrical conductivity, differential scanning calorimetry, and nuclear magnetic resonance studies have been carried out on poly(vinyl acetate) after the addition of various lithium salts. In the case of lithium triflate, the resultant polymer is poly(vinyl alcohol). Relatively large conductivites are observed after initial preparation, but these decrease with time when the material is in vacuum. The conductivities exhibit approximately Arrhenius behavior and increases with salt concentration. In addition to the conductivity, NMR, FTIR, and DSC results are presented. All results are interpreted in terms of the model of Wissbrun and Hannon where water is the solvating species.

Electrically Conducting Poly(Vinyl Acetate)

Abstract : Electrically conducting polymers have recently been the subject of intense interest. Polyacetylene has been widely studied as an electronic conductor. Ionic conductors include poly(ethylene oxide), poly(propylene oxide) and poly(ethylene succinate). In the present note, the observation of electrically conducting poly(vinyl acetate) (PVAc) is reported. Ionic conduction is inferred from the date. (Author)

Electrical Relaxation in Pply(Ethylene Oxide)

Audio frequency complex admittance has been used to investigate electrical relaxation in poly(ethylene oxide). The complex admittance measurements were performed at seventeen frequencies from 10 Hz to 100 kHz in approximately equal logarithmic intervals using a fully automated dielectric spectrometer and measurements were performed in vacuum over the temperature range 5.5 to 350 K. Two relaxations are observed at low temperatures which are consistent with the literature. In order to gain new information concerning the ¿ relaxation, measurements were made at -94, -91, and -88 ° C at pressures up to 0.2 GPa. The shift in the peak frequency with pressure, and hence the activation volume, are found to be extremely small. This result combined with other work implies that the relaxation is associated with the motion of very small segments of the polymer chain.

Thermally stimulated depolarization currents and ionic conductivity of cubic lead fluoride containing small rare earth ions

Abstract This work is concerned with thermally stimulated depolarization current (TSDC) and ionic conductivity studies in lead fluoride containing the small rare earths Dy, Ho, Er and Yb. The TSDC scans from 80 to 300 K show two peaks. For Pb1−xErxF2+x one is located at 106 K, and another, which is much stronger, occurs at about 160 K. The former is associated with a dipolar defect containing at least two rare earths and the latter is attributed to the development of F− space charge during polarization of the sample. The activation energies obtained from both the high temperature TSDC peak and the ionic conductivity are the same, which corroborates the latter assignment. In addition, the ionic conductivity is shown to be independent of concentration. Those results can be understood of rare earth clustering, which is either absent or is unobservable dielectrically for large rare earths such as lanthanum, occurs extensively even at very low concentrations of the small rare earths. The explanation is that th...