Chemistry Reference
In-Depth Information
a
b
c
1000
10
5
51°C
52°C
800
10
5
600
10
4
10
4
100
10
3
0
2.13 2.14 2.15 2.16 2.17
2.10
2.15
2.20
20
30
40
50
60
70
q (nm
−
1
)
q (nm
−
1
)
T (°C)
Fig. 16 Smectic-nematic transition in E60/40 5% as studied with high-resolution X-ray diffrac-
tion. Lineshape (a) just below and (b) just above the transition temperature,
T
NA
,of52
C. The
solid lines
are fits to a Lorentzian. (c) Domain size
L
below
T
NA
and correlation length x from a
Lorentzian fit above
T
NA
.
Vertical lines
indicate
T
NA
and
T
IN
a
b
30
60
50
20
40
30
E60 / 40 10 %
E70 / 30 10 %
10
20
10
0
0
20
30
40
50
60
70
20
30
40
50
60
70
T (°C)
T (°C)
Fig. 17 Correlation length vs. temperature from Lorentzian fits to the lineshape of the smectic
peak at various temperatures for the samples E70/30 and E60/40 for 10% crosslinks.
Vertical lines
indicate the original SmA-N and N-I transition temperatures of the corresponding 5% samples
can be well described by a simple Lorentzian corresponding to a disordered state.
For E70/30, the correlation length x increases with decreasing temperature continu-
ously from 5 nm to about 50 nm, and then saturates. The latter value corresponds
to correlation over about 18 smectic layers. The temperature dependence of x as
the subtle asymmetry in the X-ray profile, which is related to a small shift of the
maximum of the mosaic spread in the sample. We assume that below the singular
point E70/30 forms a randomly disordered smectic-like state, with some memory of
the distribution of layer normals, that transforms to a nematic state with thermal
layer fluctuations only.
For the more nematogenic compound E60/40 with 10% crosslinks, no inflection
Search WWH ::
Custom Search