Chemistry Reference
In-Depth Information
Fig. 4 Influence of counterion on the osmotic coefficient of aqueous solutions of poly(ethylene
sulfonates) at 25
C from isopiestic measurements by Ise and Asai [
37
]:
open squares
N(
n
C
4
H
9
)
4
;
open diamonds
N(
n
C
3
H
7
)
4
;
open triangles
N(
n
C
2
H
5
)
4
;
times
N(
n
CH
3
)
4
;
open
circles
N(CH
3
)
3
CH
2
C
6
H
5
;+, NH
4
;
filled diamonds
H;
closed circles
Li;
closed triangles
K
Figures
3
and
4
show some typical examples of the influence of the nature of the
counterion of a polyelectrolyte on the osmotic coefficient. The osmotic coefficient is
typically very small for inorganic counterions, but it can be increased by a factor of
about 10 by organic counterions, for the same temperature and polyelectrolyte
monomer-group molality. Figure
4
shows that the osmotic coefficient of an aqueous
solution of a poly (ethylene sulfonate) increases in the counterion series
K
+
,Li
+
,H
+
,
NH
4
,
N
+
(CH
3
)
3
CH
2
C
6
H
5
,N
+
(CH
3
)
4
,N
+
(C
2
H
5
)
4
,N
+
(
n
-C
3
H
7
)
4
, and N
+
(
n
-C
4
H
9
)
4
.
3.2 Aqueous Solutions of a Single Polyelectrolyte and a Low
Molecular Weight Strong Electrolyte
There have been many investigations on the influence of a low molecular weight
strong electrolyte on the thermodynamic properties of an aqueous solution of a
polyelectrolyte. A survey on literature data is given in Table
5
. The experimental
methods already mentioned above are also common for investigating aqueous solu-
tions of both a polyelectrolyte and a salt. However, also equilibrium dialysis (EQDIA)
and EMF-measurements with ion-selective electrodes have been used in such experi-
mental investigations. In EQDIA, an aqueous polyelectrolyte solution and an aqueous
solution of a lowmolecular weight salt are separated by a membrane that is permeable
to water as well as to the ions of the salt and the counterions of the polyelectrolyte. In
phase equilibrium, the concentration of the free ions in the coexisting phases are
