Chemistry Reference
In-Depth Information
ˆ
ð
0
Þ
is the configurational parameter for the polyion when it is dissolved in
pure water and
where
ˆ
ð
1
Þ
is an adjustable parameter, proved to be sufficient to describe
that influence.
Predictions from the model for the osmotic coefficient can be made when the
binary parameter between nondissociated repeating units and the counterion of the
low molecular weight salt, as well as the influence of that salt on the configurational
parameter
b
* are neglected. Figure
16
shows comparisons between experimental
data and calculation results for the osmotic coefficient for aqueous solutions of a
sodium poly(acrylate) (NaPA 15) and NaCl. The osmotic coefficient (on molality
scale) is plotted versus the “overall solute molality”
P
m
i
that is defined as:
X
m
i
¼
2
m
MX
þð
1
þ nÞ
m
p
:
(182)
The experimental results for the mixed solute systems are shown for a constant
activity of water. The results extend from the polyelectrolyte (i.e., salt-free) system
to the (NaCl
water) system. The top diagram of Fig.
16
shows the comparison
with prediction results, i.e., the calculations were performed setting
a
p;Cl
¼
þ
0 and
ˆ
ð
1
Þ
¼
0. The middle diagram of Fig.
16
shows the comparison with correlation
results when the influence of NaCl on the configurational parameter
b
* is neglected
(i.e., adjusting only
a
p;Cl
). The bottom diagram of Fig.
16
shows that the best
agreement is achieved by adjusting both parameters. With those parameter an
essential improvement is achieved, in particular at high concentrations (i.e., at
low water activities). Figure
17
shows a comparison between the correlation results
Fig. 17 Osmotic coefficient of aqueous solutions of NH
4
PA 10 and NaCl at 298.2K. Experimental
results are shown with
symbols
.
Dashed line
correlation results for system without salt;
dotted line
correlation results for system without polyelectrolyte;
solid lines
lines of constant water activity
[
116
]
