of scaling relations, the separate influences of number density and ionic mobility on
the ion conductivity will be discussed.
3 Conductivity Spectra of Dried PEC: Dependence
on Temperature
3.1 Isothermal Conductivity Spectra of PEC
This part focuses on the properties of PEC materials in the completely dry state.
Typically, these complexes are dialyzed, dried, and compressed into solid pellets of
roughly 1 mm thickness prior to impedance experiments. PEC with x ! 0.5 are
cotton-like, white homogeneous solid substances. For PDADMAC-rich complexes
(x < 0.5) we can distinguish two phases: one phase is cotton-like (similar to that of
the PSS-rich compositions) and the second is a hard salt-like phase. The two-phase
PEC materials were thoroughly milled and mixed before use [40]. DSC results
showed no indication for phase separation in any of the PEC, but confirmed the
glassy character of the investigated samples. This implies that the second phase
present in the PDADMAC-rich complexes does not undergo any phase transition
within the investigated temperature range. Solid-state NMR studies on dried
AlkaliPSS-rich PEC (with 0.53 x < 1) clearly showed that the alkali ions are
randomly distributed in the PSS-rich PEC, indicating a non-segregated structure
[45]. The finding that dried PSS-rich PEC are homogeneous, whereas PDADMACrich are not, corresponds to results obtained by Carrie `re et al. for hydrated
complexes. From the asymmetric behavior of the osmotic coefficient of hydrated
PEC in dependence of mixing ratio, x, it was concluded that polyanion-rich PEC are
homogeneous, whereas polycation-rich PEC undergo a microphase separation of
neutral from anion-rich regions [46]. More experimental details on sample preparation, characterization and experimental procedures are given in the literature [40].
As a typical example, Fig. 5 shows data of xNaPSS · (1 À x) PDADMAC for
x ¼ 0.40 and 0.60 [40]. The low-frequency part of each spectrum is determined by
a frequency regime where the conductivity is independent of frequency. The
corresponding conductivity value of each isotherm can be identified with the dc
conductivity; the values will be discussed in detail in Sect. 3.2.
With increasing temperature, T, the conductivity values increase and the onset of
conductivity dispersion shifts to higher frequency. The latter effect can be detected
in the PEM spectra of Fig. 4b and it is well known to also exist in other ionconducting materials. In Fig. 5, the common definition σ
0 (ν*) ¼ 2σ dc is used for the
onset frequency, ν*, which characterizes the transition from the dc into the dispersive regime. In both PEC materials, the onset points are on a straight line, but their
slope differs. For x ¼ 0.40, the slope is smaller than one, for x ¼ 0.60 it exceeds
one. This is one of the marked differences between the spectra of PEC that are rich
in PDADMAC and those that are rich in NaPSS. The implications of this difference
will be further discussed in Sect. 5.2 in the context of scaling principles.
Ion Conduction in Solid Polyelectrolyte Complex Materials
107
the ion conductivity will be discussed.
3 Conductivity Spectra of Dried PEC: Dependence
on Temperature
3.1 Isothermal Conductivity Spectra of PEC
This part focuses on the properties of PEC materials in the completely dry state.
Typically, these complexes are dialyzed, dried, and compressed into solid pellets of
roughly 1 mm thickness prior to impedance experiments. PEC with x ! 0.5 are
cotton-like, white homogeneous solid substances. For PDADMAC-rich complexes
(x < 0.5) we can distinguish two phases: one phase is cotton-like (similar to that of
the PSS-rich compositions) and the second is a hard salt-like phase. The two-phase
PEC materials were thoroughly milled and mixed before use [40]. DSC results
showed no indication for phase separation in any of the PEC, but confirmed the
glassy character of the investigated samples. This implies that the second phase
present in the PDADMAC-rich complexes does not undergo any phase transition
within the investigated temperature range. Solid-state NMR studies on dried
AlkaliPSS-rich PEC (with 0.53 x < 1) clearly showed that the alkali ions are
randomly distributed in the PSS-rich PEC, indicating a non-segregated structure
[45]. The finding that dried PSS-rich PEC are homogeneous, whereas PDADMACrich are not, corresponds to results obtained by Carrie `re et al. for hydrated
complexes. From the asymmetric behavior of the osmotic coefficient of hydrated
PEC in dependence of mixing ratio, x, it was concluded that polyanion-rich PEC are
homogeneous, whereas polycation-rich PEC undergo a microphase separation of
neutral from anion-rich regions [46]. More experimental details on sample preparation, characterization and experimental procedures are given in the literature [40].
As a typical example, Fig. 5 shows data of xNaPSS · (1 À x) PDADMAC for
x ¼ 0.40 and 0.60 [40]. The low-frequency part of each spectrum is determined by
a frequency regime where the conductivity is independent of frequency. The
corresponding conductivity value of each isotherm can be identified with the dc
conductivity; the values will be discussed in detail in Sect. 3.2.
With increasing temperature, T, the conductivity values increase and the onset of
conductivity dispersion shifts to higher frequency. The latter effect can be detected
in the PEM spectra of Fig. 4b and it is well known to also exist in other ionconducting materials. In Fig. 5, the common definition σ
0 (ν*) ¼ 2σ dc is used for the
onset frequency, ν*, which characterizes the transition from the dc into the dispersive regime. In both PEC materials, the onset points are on a straight line, but their
slope differs. For x ¼ 0.40, the slope is smaller than one, for x ¼ 0.60 it exceeds
one. This is one of the marked differences between the spectra of PEC that are rich
in PDADMAC and those that are rich in NaPSS. The implications of this difference
will be further discussed in Sect. 5.2 in the context of scaling principles.
Ion Conduction in Solid Polyelectrolyte Complex Materials
107