Chemistry Reference
In-Depth Information
Fig. 15 Osmotic coefficient of aqueous solutions of poly(sodium methacrylate) at 298.2 K with
two different molecular masses. Experimental results:
closed squares
NaPMA 6;
open squares
NaPMA 15. Correlation results:
solid line
NaPMA 6;
dashed line
NaPMA 15 [
116
]
Figure
15
shows a typical example for correlation of experimental results for the
osmotic coefficient (on molality scale) of aqueous solutions of poly(sodium meth-
acrylate).
For the calculation of the thermodynamic properties of an aqueous solution of a
single polyion that additionally contains a low molecular weight strong electrolyte,
some more model parameters are required. The volume and surface parameters of
the ions of the strong electrolyte are also approximated by the parameters of water.
Therefore, for an aqueous solution of the single salt the model does not differ from
Pitzer's model, and for a large number of salts the binary interaction parameters
a
ð
0
Þ
MX
and
a
ð
1
Þ
MX
are available in the literature. All further interaction parameters (i.e.,
between cations and anions of the salt on one side and groups and counterions from
the polyion on the other side) are also set to zero, with the exception of a single
parameter. That parameter accounts for interactions between that ion of
MX
that
carries an electrical charge of the opposite sign as the counterion of the polyion on
one side, and the neutral group of the polyelectrolyte (i.e.,
A
or
C
) on the other side.
For example, if NaCl is added to an aqueous solution of poly(sodium methacrylate),
the only additional interaction parameter is
a
ð
0
Þ
A
;
Cl
(=
a
p;
Cl
). Because the configuration
of the polyion in the aqueous salt-containing solution might differ from that in the
salt-free solution, it might be advantageous to consider the influence of the low
molecular weight salt on the polyion's configuration parameter
b
*. An empirical
relation such as:
m
MX
m
o
b
¼
ˆ
ð
0
Þ
þ
ˆ
ð
1
Þ
;
(181)
