Chemistry Reference
In-Depth Information
Fig. 9 Phase diagram
(demixing into two liquid
phases) of the system CH/PS
for the indicated molar
masses of the polymer (kg/
mol). Cloud points (
open
symbols
) and critical points
(
stars
) are taken from the
literature [
45
]. The data for
the high temperatures refer to
the equilibrium vapor
pressure of the solvent.
Binodals (
solid lines
) and
spinodals (
dotted lines
) were
calculated as described in the
text by means of the
temperature dependent
parameters [
46
] z and n
37
510
97.2
500
400
CH / PS
490
¥
2700 kg / mol
300
200
97.2
290
37
280
0.0
0.1
0.2
j
the method of the direct minimization of the Gibbs energy [
19
], instead of equality of
the chemical potentials of the components as the equilibrium condition.
The agreement of information concerning the composition dependence of the
Flory Huggins interaction parameter obtained from different sources is demon-
strated by means of Fig.
10
. The data points display the results of vapor pressure
measurements and the dashed line stems from the evaluation of critical demixing
data described above. The interaction parameter is calculated according to (
6
), (
5
),
and (
32
) by reading the z and n values from figure 2 of [
46
] for 308 K, setting l
¼
0.5 and
E
¼
0.847. To the author's knowledge, this is the first time that liquid/gas
and liquid/liquid phase equilibria have been modeled accurately by the same set of
parameters, where only two were adjusted to the experimental data in the present
case.
For some technical processes and polymer applications, pressure represents an
important variable. For this reason, the extent to which the present approach is
suited to describe pressure effects was checked. By means of demixing data as a
function of pressure published for the system
trans
-decalin/PS [
49
] it was shown
[
46
] that (
32
) is also apt for that purpose.
The systems
n
-butane/1,4-polybutadiene (98% cis) [
n
-C
4
/1,4-PB] and
n
-butane/
1,2-polybutadiene [
n
-C
4
/1,2-PB] are the next examples for the modeling of Flory
Huggins interaction parameters [
50
]. In this case, it appeared particularly interest-
ing to understand why 1,2-PB is totally miscible with
n
-C
4
but 1,4-PB is not.
In these experiments we measured the absolute vapor pressures (i.e., not using
