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(a) Molecular orientation
(b) Director orientation
SIDE VIEW OF DIRECTOR
n
n
n
CL
CL
DL
(c)
E+
(d)
E-
(e)
D
C
Figure 2.18
(a) Cross-sectional view of a discotic onion texture. (b) Corresponding
radial director
n
orientation. (c-e) The right panel shows the side view of the three
possible director fi eld lines of the onion textures: positive escape
E
+
, negative escape
E
−
, and singular
+
1 disclination defect core
D
c
; CL denotes the centerline.
temperatures the viscosity superposes with
η
1
(N
c
)
(Chandrasekhar, 1992). This trend is identical to that observed with the viscosi-
ties of the N
c
and I in this SDS solution.
η
3
(N
c
), which is greater than
2.4.1.4 Orientation Fluctuations, Backfl ow
Thermally excited orienta-
tion fl uctuations have a relaxation time that is proportional to the viscosity of
the fl uid and to the inverse of the effective Frank elastic modulus. The orienta-
tion diffusity
D
0,
i
for splay, twist, and bend modes is
D
i
j
=Κ η
/
;
i
=
splay(11),
o
,
ii
i
j
o,
provides
twist(22), bend(33);
j
=
calamitic (C), discotic (D), measuring
D
i
information on material viscoelastic anisotropies (
K
ii
/
η
i
) and the relative mag-
j
j
/
, ,
for the different modes also refl ects the molecular
shape (disk or rod) (Santos and Amato, 1999). In addition since the transient
reorientation viscosities for splay and bend contain backfl ow information, this
important rheological process can be accessed through the orientation diffu-
sion measurements (Santos and Amato, 1999). Extensive data with potassium
nitude of the ratio
D
D
o
i
o
k
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