Chemistry Reference
In-Depth Information
150
140
130
120
110
N
C
N
D
100
I
90
80
70
60
19.5
28
36
T (C)
Figure 2.17
Apparent shear viscosity as a function of temperature for a 35/7/58 wt %
SDS/decanol/water solution obtained using capillary rheometry. The N
d
, N
c
, and I
regions are indicated. The peak viscosity regions are the result of transitional effects,
and the viscosity decrease is due to the usual Arrhenius effect. The top schematics show
corresponding side views of orientation patterns in the capillary rheometer. [Adapted
from Kuzma et al. (1989).]
η
η
η
η
η
η
-
!
2
2
2
η
=
η
=
η
181
+
−
1 12
+−
ln
4
app
E
+
app
E
−
1
1
1
1
−1
(
)
2
(
)
.
ηη
12
1
2
/
−
ηη
/
−−
1
ηη
/
η
η
0
0
21
21
1
+
2
tan
−
1
−
1
>
η
=
η
"
app
D
2
ηη
/
−
1
2
12
(2.53)
The lowest zero shear apparent viscosity is that of the singular onion textures.
For typical thermotropes it was found that
10
(de
Andrade Lima and Rey, 2003a, 2004e). Hence core restructuring can lead to
viscosity decrease. Another factor that can account for the lower N
d
viscosity
with respect to N
c
is that the viscosity of the latter is associated with a fl ow-
aligned state at low shear if the wall anchoring is along the fl ow direction.
In this case, the N
c
viscosity is just
η
=
η
≈
η
app
E
+
app
E
−
app
D
c
η
1
because the director is along the
fl ow direction and no texture appears. The LE model is consistent with experi-
mental data if 10
T
2
. In the I phase the viscosity is
α
4
(I). For calamitic thermotropes, it is found that extrapolating
η
2
(N
d
,
T
1
)
<
η
1
(N
c
,
T
2
);
T
1
<
α
4
(I) to lower
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