of ions, i.e., Na
+ ions. Spectra of x 0.50 can be fitted in a similar way. The
component describing the localized motions of charged particles is still necessary
to describe the spectra, but its contribution to the total spectra is much less pronounced than in the case of PSS-rich PEC (see also Fig. 6). In passing, we note that
the conductivity spectra of PEM can also be described by a superposition of a
MIGRATION-type contribution and a contribution that reflects strictly localized
movements. Also, in the case of PEM, the q-values are close to 2, but the bending
into the σ loc (1) plateau regime is not visible at the measured frequencies [47].
4 RH-Dependent Spectra
The work by Michaels [2, 3] and Durstock and Rubner[27], described in the
previous section showed that permittivity (and therefore also conductivity) spectra
of PEC and PEM strongly differ for dried and hydrated materials. The reason is that
these materials take up water when exposed to a humid atmosphere. In order to
relate humidity and water content, several studies have dealt with the water uptake
of multilayers, employing reflectivity techniques, [64, 65] or of complexes,
employing gravimetric analysis [66].
To investigate the RH-dependent conductivity, studies on PEC [66, 67] and
PEM [30, 39] were performed. In this work, the composition and the type or amount
of alkali ions were varied and samples were equilibrated at different RH. Here, we
discuss the RH dependence for the two PEC systems xNaPSS·(1 À x) PDADMAC
and xCsPSS·(1 À x) PDADMAC [66]. The results refer to compositions x ! 0.50,
i.e., for systems that are either stoichiometric or have an excess of alkali ions. As
outlined before, such PEC can be considered as homogenous materials.
4.1 Conductivity Spectra of PEC at Constant RH
Figure 14a,b shows a log–log plot of the real part of the conductivity spectra σ
0
against experimental frequency ν of NaPEC and CsPEC, taken after equilibration at
different RH values. At low RH (29% and 46%) no appreciable electrode polarization effects are seen. However, with increasing RH, polarization effects move into
the experimental frequency window.
For both kinds of complexes (NaPEC and CsPEC) and over the entire humidity
regime, a well-defined low-frequency plateau is observed, where the conductivity is
independent of frequency and can be identified with the dc conductivity. With
increasing RH, the dc plateau moves towards higher conductivity values. At
frequencies higher than those of the dc regime, the conductivity increases monotonously with frequency at all RH. Moreover, the onset of this dispersion shifts
towards higher frequency with increasing humidity. The onset of dispersion is
characterized by the onset frequency ν* (shown as star symbols in Fig. 14). These
Ion Conduction in Solid Polyelectrolyte Complex Materials
119
+ ions. Spectra of x 0.50 can be fitted in a similar way. The
component describing the localized motions of charged particles is still necessary
to describe the spectra, but its contribution to the total spectra is much less pronounced than in the case of PSS-rich PEC (see also Fig. 6). In passing, we note that
the conductivity spectra of PEM can also be described by a superposition of a
MIGRATION-type contribution and a contribution that reflects strictly localized
movements. Also, in the case of PEM, the q-values are close to 2, but the bending
into the σ loc (1) plateau regime is not visible at the measured frequencies [47].
4 RH-Dependent Spectra
The work by Michaels [2, 3] and Durstock and Rubner[27], described in the
previous section showed that permittivity (and therefore also conductivity) spectra
of PEC and PEM strongly differ for dried and hydrated materials. The reason is that
these materials take up water when exposed to a humid atmosphere. In order to
relate humidity and water content, several studies have dealt with the water uptake
of multilayers, employing reflectivity techniques, [64, 65] or of complexes,
employing gravimetric analysis [66].
To investigate the RH-dependent conductivity, studies on PEC [66, 67] and
PEM [30, 39] were performed. In this work, the composition and the type or amount
of alkali ions were varied and samples were equilibrated at different RH. Here, we
discuss the RH dependence for the two PEC systems xNaPSS·(1 À x) PDADMAC
and xCsPSS·(1 À x) PDADMAC [66]. The results refer to compositions x ! 0.50,
i.e., for systems that are either stoichiometric or have an excess of alkali ions. As
outlined before, such PEC can be considered as homogenous materials.
4.1 Conductivity Spectra of PEC at Constant RH
Figure 14a,b shows a log–log plot of the real part of the conductivity spectra σ
0
against experimental frequency ν of NaPEC and CsPEC, taken after equilibration at
different RH values. At low RH (29% and 46%) no appreciable electrode polarization effects are seen. However, with increasing RH, polarization effects move into
the experimental frequency window.
For both kinds of complexes (NaPEC and CsPEC) and over the entire humidity
regime, a well-defined low-frequency plateau is observed, where the conductivity is
independent of frequency and can be identified with the dc conductivity. With
increasing RH, the dc plateau moves towards higher conductivity values. At
frequencies higher than those of the dc regime, the conductivity increases monotonously with frequency at all RH. Moreover, the onset of this dispersion shifts
towards higher frequency with increasing humidity. The onset of dispersion is
characterized by the onset frequency ν* (shown as star symbols in Fig. 14). These
Ion Conduction in Solid Polyelectrolyte Complex Materials
119