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a
b
10
1
polymer
1
st
order
polymer
2
nd
order
10
-1
10
0
10
-2
10
-1
10
-3
10
-2
10
-4
1.3
1.4
1.5
1.6
2.8
2.9
3.0
q (nm
−
1
)
q
z
(nm
−
1
)
c
d
10
-2
elastomer
1
st
order
elastomer
2
nd
order
10
-1
10
-2
10
-3
10
-3
2.4
2.6
2.8
3.0
3.2
3.4
1.0
1.2
1.4
1.6
1.8
q
z
(nm
−
1
)
q (nm
−
1
)
Fig. 19 First- and second-order peaks of MeHQ-pol (a, b) and MeHQ-el (c, d).
Dashed lines
of the successive harmonics increases as
n
2
. This leaves as the most plausible
explanation that the Lorentzian lineshape is due to a broad exponential-like
distribution of domain sizes in the sample. Such situations have been well docu-
mented in powder diffraction (see, for example, [
156
]). The specific nature of the
distribution (as compared to other smectic systems) could arise from the direct
coupling between polymer defects and smectic layer correlations typical for main-
indicate that during the formation of a monodomain sample simple hairpins are
probably removed by the mechanical strain and might play only a minor role [
68
].
On the other hand, this argument does not hold for entangled hairpins as depicted
in Fig.
4d
. The presence of such defects would be compatible with a plateau in the
stress-strain curve. Additionally, chain ends may play a role. Analogous to the
situation described for the nematic phase [
39
],thesecouldalsoleadtolocal
chains themselves contribute to the building of the smectic layers. Due to disper-
sion of the polymer chain length, the layered structure in the direction along layer
normal cannot be terminated at any arbitrary place, thus leading to finite-size
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