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density drives the transition towards the supercritical regime in various types of
LCEs (both side- and main-chain).
In that study, conventional polysiloxane-based side-chain LCEs were used; the
chemical formulae of their components (mesogen, polymer backbone, crosslinkers)
are shown in Fig.
17a
. First, the effect of the concentration of the rod-like bifunc-
tional crosslinker denoted as V6 was studied. LCE samples with crosslinking
densities
x
SC
equal to 0.075, 0.105, 0.125, 0.150 and 0.160 were prepared and
investigated. Here,
x
SC
denotes the coverage of the active groups of the siloxane-
based polymer chain and is (in the case of full coverage) equal to the mol% of
crosslinker
crosslinker functionality. Additionally, LCEs of the same composi-
tion but with a trifunctional crosslinker, denoted as V3, were also prepared. The
investigated crosslinking densities in this case were equal to 0.075, 0.105 and 0.125.
In order to further investigate the role of the crosslinking topology, a similar
study was performed for main-chain LCEs (the components' chemical formulas are
shown in Fig.
17b
). The crosslinking of the main-chain LCEs was realized by a
pentafunctional cyclic siloxane crosslinker (denoted as HD5) [
7
]. LCEs with cross-
linker-mesogen molar ratios
x
MC
of 0.025, 0.04, 0.06, 0.08 and 0.12 were prepared
and investigated. In contrast to the side-chain LCEs, in main-chain LCEs the
crosslinking density is characterized by
x
MC,
which is the ratio of the number of
crosslinkers to the number of mesogens. Obviously, due to the different crosslinker
O
O
O
COO
O
O
O
O
Si
H
O
O
D
n
O
O
CN
D
D
O
D
O
O
O
D
O
O
D
H
O
O
Si
H
H
Si
O
O
O
O
H
Si
O
Si
V6 crosslinker
Si
O
O
Si
O
H
Si
O
H
H
V3 crosslinker
O
HD5 crosslinker
O
Fig. 17 Schematic drawing (only illustrative) of the (a) side-chain and (b) main-chain LCEs used
in this study together with the chemical formulas of the LCE components and deuterated probe
molecules. The various crosslinkers are denoted as V6, V3 and HD5
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