Chemistry Reference
In-Depth Information
x
MC
0.
0
25
0
.05
0
0.0
7
5
0
.
100
0.1
2
5
V6 calorimetry
V6 NMR
V3 calorimetry
HD5 calorimetry
0.6
0.4
0.2
0.0
0.06
0.08
0.10
0.12
0.14
0.16
x
SC
Fig. 21 Values of latent heat (
L
) for side-chain LCEs (with V6 and V3 crosslinkers) and main-
chain LCEs (HD5 crosslinker) for various values of crosslinking density
x
SC
(
bottom axis
, applies
to side-chains) and crosslinker concentration
x
MC
(
top axis
, applies to main-chains). The latent-
coexisting nematic and paranematic phases at the transition temperature
T
PN-N
,
whereas
1 mg/mm
3
). The absolute value of
r
is the density of the LCE network (
r
the LdG parameter
here represents a scaling parameter whose optimal value is
adjusted by comparing the measured (calorimetry) and the calculated (NMR)
calculated values of
L
on the crosslinking density of LCE exhibit a very good
agreement.
Taking into account the obtained values of the
w
G
(
G
) parameters, the recorded
LCEs with lower crosslinker concentrations (
x
SC
≲
a
0.075,
x
MC
≲
0.04) exhibit a
prevalently subcritical behaviour, whereas the LCEs with higher crosslinker con-
centrations (
x
SC
≳
0.12) exhibit a prevalently supercritical behaviour.
In LCEs with intermediate concentrations the smeared criticality is most evident.
Although being on average supercritical (judging from the value of
0.15,
x
MC
≳
/
G
C
), the
features of below-criticality such as a nonzero
L
and a pronounced broadening of
the
2
H-NMR spectral line at the phase transition are still present.
Thus, the increase of the crosslinking density in the LCEs results in a shift of
their phase-transition behaviour towards and beyond supercritical. As this trend is
now confirmed for both the side- and main-chain nematic LCEs, i.e. two LCE
families with drastically different crosslinking topologies, it can be anticipated that
the link between the crosslinking concentration and the phase-transition criticality
holds universally for most types of LCEs.
hGi
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