Chemistry Reference
In-Depth Information
3.0
2.6
2.2
1.8
1.4
1.0
0.6
0
1000
2000
3000
PDMS M
n
4000
5000
6000
Fig. 4 Experimental interfacial tension at 25
C between PDMS and PBD 1000 as a function of
the
M
n
of PDMS.
Solid line
represents the best fit to a
M
n
1
dependence and the
dotted line
is the
fit for a
M
n
0.5
dependence [
19
,
20
]
with four poly(dimethyl siloxanes), PDMS, are shown in Fig.
3
as a function of
temperature. Interfacial tension decreases almost linearly with temperature with
temperature coefficients of 0.75
10
2
dyn/(cm
C).
The effect of PDMS molecular weight on the interfacial tension at constant
temperature for a constant molecular weight of PBD (
M
n
¼
2
to 1.2
10
1.07)
is illustrated in Fig.
4
. The molecular weight dependence was obtained by perfor-
ming nonlinear least-squares regression of the data to an expression of the form
g ¼ g
1
1
980,
M
w
/
M
n
¼
. This analysis yielded
z
0.54 for the present PDMS/PBD
system of the specific range of low molecular weights.
The interfacial tension data for blends of PS of various molecular weights versus
a poly(ethyl ethylene) (PBDH 4080;
M
n
¼
k
int
M
z
¼
n
1.04) exhibited a similar
behavior with temperature, with temperature coefficients 0.9
4800,
M
w
/
M
n
¼
10
2
dyn/(cm
C), and, qualitatively, with molecular weight. However, fitting the data to
the expression
g ¼ g
1
2
to 1.5
10
yielded
z
k
int
M
z
n
1
¼
0.68 for PS molecular weights
between 2200 and 10,200.
The measurements for the blends of PS and poly(methyl methacrylate) (PMMA;
M
n
¼
10,000,
M
w
/
M
n
¼
1.05) cover the broadest range of molecular weights
(Fig.
5
). For
this
system, nonlinear fit of
the data to the expression
resulted in
z
k
int
M
z
g ¼ g
1
1
¼
0.90 for PS molecular weights between 2200
n
and 43,700.
These values for the exponent
z
should be taken with caution because of
experimental errors. However, it was pointed out [
20
] that the smallest value for
z
