of ions results from a significant increase in the ion mobility. The mobility increase
goes along with a decrease in the activation enthalpy connected with the long-range
ion transport [49]. Although the simulations of Bunde, Ingram, and Maass refer to
inorganic glassy conductors, the concept can be transferred to PSS-rich PEC.
Ion transport results if ions move into vacant sites that were recently vacated by
other ions. The higher the ion content, the more of such just-vacated sites exist and
therefore the ion mobility increases. This means that the number density of mobile
ions strongly influences the energy landscape in which ions move. This change
is also reflected in the activation enthalpy as a parameter characterizing the longrange ion transport. One should not misinterpret ΔH as a simple activation barrier
between two different ion sites; this enthalpy is connected with successful ionic
hopping processes causing long-range transport. Therefore, ΔH reflects thermally
activated movements of initially hopping ions as well as correlated movements of
neighboring surrounding ions.
The three different alkali types of PSS-rich PEC just discussed bear some
similarity to inorganic cation-conducting glassy materials. The x-dependence of
σ dc and ΔH for a given type of alkali ion is itself a strong indication that the alkali
ions are the most mobile species in dried PSS-rich PEC. This conclusion is also
strongly supported by the dependence of σ dc and ΔH on the type of cation for
different alkali PEC with constant x. The fact that these quantities correlate so well
with the ionic radius clearly shows that PSS-rich PEC are alkali cation-conducting
materials.
In PDAMAC-rich PEC, the situation differs. For a given alkali PEC-system, the
conductivity increases and the activation enthalpy decreases when changing x from
0.40 to 0.50. Although these changes are less pronounced than those resulting from
a change of x from0.50 to 0.60, they still indicate conduction of residual cations
rather than conduction of chloride ions. If Cl
À ions were the most mobile species,
one would expect the conductivity of PEC with x ¼ 0.40 to be higher than that of
x ¼ 0.50, which is not the case. Instead, the conductivity monotonously increases
with PSS content. Thus, two conclusions are obtained: (1) The mobility of the Cl
À
ions is negligible and for all compositions the conductivity is dominated by the
contribution of the alkali cations. (2) The number of residual alkali ions in PEC with
x 0.5 slightly increases with PSS content and, as a result, the conductivity
increases and the activation enthalpy decreases slightly with increasing x.
The presented results, however, shed even more light on the type of charge
carriers in chloride-rich PEC: even for x 0.50, the dc conductivity depends on the
type of alkali ion. This can be taken as a direct proof that in PEC, where Cl
À ions
should be the majority extrinsic charge carriers, residual alkali ions indeed provide
the major contribution to the overall conductivity due to their much higher mobility.
One open question is why the activation enthalpy values of PEC with x ¼ 0.50 do
not show any systematic variation with the type of alkali ion, whereas they do differ
for PEC that deviate from x ¼ 0.50. One reason for this could be that the exact
composition is hardest to control for x ¼ 0.50. Theoretically, it should be perfectly
intrinsically charge-compensated. In practice, however, the number of crosslinks
between the polyions might change slightly from sample to sample. In other words,
114
C. Cramer and M. Scho ¨nhoff
goes along with a decrease in the activation enthalpy connected with the long-range
ion transport [49]. Although the simulations of Bunde, Ingram, and Maass refer to
inorganic glassy conductors, the concept can be transferred to PSS-rich PEC.
Ion transport results if ions move into vacant sites that were recently vacated by
other ions. The higher the ion content, the more of such just-vacated sites exist and
therefore the ion mobility increases. This means that the number density of mobile
ions strongly influences the energy landscape in which ions move. This change
is also reflected in the activation enthalpy as a parameter characterizing the longrange ion transport. One should not misinterpret ΔH as a simple activation barrier
between two different ion sites; this enthalpy is connected with successful ionic
hopping processes causing long-range transport. Therefore, ΔH reflects thermally
activated movements of initially hopping ions as well as correlated movements of
neighboring surrounding ions.
The three different alkali types of PSS-rich PEC just discussed bear some
similarity to inorganic cation-conducting glassy materials. The x-dependence of
σ dc and ΔH for a given type of alkali ion is itself a strong indication that the alkali
ions are the most mobile species in dried PSS-rich PEC. This conclusion is also
strongly supported by the dependence of σ dc and ΔH on the type of cation for
different alkali PEC with constant x. The fact that these quantities correlate so well
with the ionic radius clearly shows that PSS-rich PEC are alkali cation-conducting
materials.
In PDAMAC-rich PEC, the situation differs. For a given alkali PEC-system, the
conductivity increases and the activation enthalpy decreases when changing x from
0.40 to 0.50. Although these changes are less pronounced than those resulting from
a change of x from0.50 to 0.60, they still indicate conduction of residual cations
rather than conduction of chloride ions. If Cl
À ions were the most mobile species,
one would expect the conductivity of PEC with x ¼ 0.40 to be higher than that of
x ¼ 0.50, which is not the case. Instead, the conductivity monotonously increases
with PSS content. Thus, two conclusions are obtained: (1) The mobility of the Cl
À
ions is negligible and for all compositions the conductivity is dominated by the
contribution of the alkali cations. (2) The number of residual alkali ions in PEC with
x 0.5 slightly increases with PSS content and, as a result, the conductivity
increases and the activation enthalpy decreases slightly with increasing x.
The presented results, however, shed even more light on the type of charge
carriers in chloride-rich PEC: even for x 0.50, the dc conductivity depends on the
type of alkali ion. This can be taken as a direct proof that in PEC, where Cl
À ions
should be the majority extrinsic charge carriers, residual alkali ions indeed provide
the major contribution to the overall conductivity due to their much higher mobility.
One open question is why the activation enthalpy values of PEC with x ¼ 0.50 do
not show any systematic variation with the type of alkali ion, whereas they do differ
for PEC that deviate from x ¼ 0.50. One reason for this could be that the exact
composition is hardest to control for x ¼ 0.50. Theoretically, it should be perfectly
intrinsically charge-compensated. In practice, however, the number of crosslinks
between the polyions might change slightly from sample to sample. In other words,
114
C. Cramer and M. Scho ¨nhoff