Michaels et al. [2, 3] found that the stoichiometric NaPSS/VBTAC complex,
when completely free of extraneous electrolytes, exhibits a high dc resistivity
(approximately 10
10
Ω cm). The value of ε
0 measured at 100 Hz changes from 50
to 5 (for water-saturated PEC) and from about 5 to 3 (for dried PEC) at 0.1 MHz.
When doped with simple electrolytes like NaBr, the absolute values of the complex
permittivity as well as the dependence of ε
0 and ε
00 on frequency change significantly. Figure 2 shows the influence of the dopant salt [2].
In the investigated frequency range, the dielectric loss as well as the
corresponding conductivity σ
0 increase with dopant concentration by several
oders of magnitude. For undoped PEC, the conductivity spectrum only shows a
dispersive regime. With higher dopant concentration, a dc plateau becomes visible.
The spectra show strong similarity with those of Fig. 1b. Though not stated by the
authors, the superimposed slight decay of σ
0 towards smaller frequencies seen for
0.23 and 0.46 is propably due to polarization effects, which can never be avoided
when blocking electrodes are used.
Michaels et al. also determined the influence of the RH on the permittivity of
polyelectrolyte complexes (see Fig. 3). The data points of Fig. 3a have been taken
from Fig. 9 of [3]; the dashed lines as well as the real part of the conductivity have been
calculated for this review. The data show that the dc conductivity increases significantly with RH. Also here, polarization effects are detectable at low frequencies.
Michaels et al. concluded from their results that the permittivity spectra mostly
arise from minor displacements of the ionic side groups of the macromolecules.
Traces of small ions, which are also present in nominally intrinsically compensated
complexes, are claimed to be also involved in these local motions, but their
long-range mobility is rather small. Water “loosens” the structure and facilitates
ion motion.
2.3 The Structural Analogue: Polyelectrolyte Multilayers
and Their Conductivity
After the very early work by Michaels et al., the next frequency-dependent permittivity spectra of solid polyelectrolyte materials were only published in 2001 by
Durstock and Rubner, who studied PEM prepared by the layer-by-layer technique
[27]. The investigated PEM were made of the polycation poly(allylamine hydrochloride) (PAH) and the polyanions PAA or PSS. The authors investigated very
systematically the influences of parameters like pH, temperature, salt content, and
RH (wet and dry PEM) on the real and imaginary part of the permittivity.
In Fig. 4, we see how temperature influences the shape and the values of the
dielectric loss and the corresponding conductivity spectra of PAH/PSS PEM. At a
given frequency, the conductivity increases with temperature. One also sees that the
transition into the dispersive regime shifts to higher frequencies when the temperature is raised. Electrode polarization effects are visible at the lowest frequencies.
Ion Conduction in Solid Polyelectrolyte Complex Materials
105
when completely free of extraneous electrolytes, exhibits a high dc resistivity
(approximately 10
10
Ω cm). The value of ε
0 measured at 100 Hz changes from 50
to 5 (for water-saturated PEC) and from about 5 to 3 (for dried PEC) at 0.1 MHz.
When doped with simple electrolytes like NaBr, the absolute values of the complex
permittivity as well as the dependence of ε
0 and ε
00 on frequency change significantly. Figure 2 shows the influence of the dopant salt [2].
In the investigated frequency range, the dielectric loss as well as the
corresponding conductivity σ
0 increase with dopant concentration by several
oders of magnitude. For undoped PEC, the conductivity spectrum only shows a
dispersive regime. With higher dopant concentration, a dc plateau becomes visible.
The spectra show strong similarity with those of Fig. 1b. Though not stated by the
authors, the superimposed slight decay of σ
0 towards smaller frequencies seen for
0.23 and 0.46 is propably due to polarization effects, which can never be avoided
when blocking electrodes are used.
Michaels et al. also determined the influence of the RH on the permittivity of
polyelectrolyte complexes (see Fig. 3). The data points of Fig. 3a have been taken
from Fig. 9 of [3]; the dashed lines as well as the real part of the conductivity have been
calculated for this review. The data show that the dc conductivity increases significantly with RH. Also here, polarization effects are detectable at low frequencies.
Michaels et al. concluded from their results that the permittivity spectra mostly
arise from minor displacements of the ionic side groups of the macromolecules.
Traces of small ions, which are also present in nominally intrinsically compensated
complexes, are claimed to be also involved in these local motions, but their
long-range mobility is rather small. Water “loosens” the structure and facilitates
ion motion.
2.3 The Structural Analogue: Polyelectrolyte Multilayers
and Their Conductivity
After the very early work by Michaels et al., the next frequency-dependent permittivity spectra of solid polyelectrolyte materials were only published in 2001 by
Durstock and Rubner, who studied PEM prepared by the layer-by-layer technique
[27]. The investigated PEM were made of the polycation poly(allylamine hydrochloride) (PAH) and the polyanions PAA or PSS. The authors investigated very
systematically the influences of parameters like pH, temperature, salt content, and
RH (wet and dry PEM) on the real and imaginary part of the permittivity.
In Fig. 4, we see how temperature influences the shape and the values of the
dielectric loss and the corresponding conductivity spectra of PAH/PSS PEM. At a
given frequency, the conductivity increases with temperature. One also sees that the
transition into the dispersive regime shifts to higher frequencies when the temperature is raised. Electrode polarization effects are visible at the lowest frequencies.
Ion Conduction in Solid Polyelectrolyte Complex Materials
105