Chemistry Reference
In-Depth Information
20 °C up
40 °C up
70 °C up
80 °C up
90 °C up
90 °C dowm
80 °C dowm
70 °C dowm
40 °C dowm
20 °C dowm
(a)
(b)
Without MC/KC
With MC/KC
10
0
10
0
CREAMING AND
PHASE SEPARATION
10
−1
0.0
10
−1
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0.5
1.0
1.5
2.0
2.5
3.0
(nm
−1
)
(nm
−1
)
q
q
Figure 6.13
Enhanced ISAsome stability due to being embedded in hydrogels. SAXS
studies with a stepwise temperature scan of 20-90-20°C on the DU/TC system with
δ
5% of the dispersed phase. (a) Free ISAsomes (without gelator) show
phase separation due to creaming at higher temperatures; during the downward scan,
the curves do not show the same appearance as during the upward scan (see lower set
of broken curves). (b) With 2% gelator (MC : KC 1 : 1), the absence of creaming can be
clearly observed from the downward scan, thus revealing the high-temperature stabiliz-
ing effect of the MC-KC (1 : 1) polymer mixture on the ISAsomes.
=
85 and
ϕ
=
occasionally showed more signifi cant effects (Guillot et al., 2009b). Hexo-
somes (DU/LM system,
83.3) in KC were investigated using SAXS (Fig.
6.12b), which showed that the lattice parameter of the hexagonal nanostruc-
ture increased from 5.65 to 5.75 nm. However, in a further study, the KC-
loaded EME (DU/LM system,
δ
=
54.3) was converted into the micellar cubic
Fd3m phase at 25°C, as shown by curve
c
in Figure 6.12 c.
An important advantage of the incorporation of ISAsomes into such gelled
polymer systems is the increase in their stability. This is particularly true at
higher temperature, when free-ISAsome systems undergo rather rapid cream-
ing (Fig. 6.13a). The addition of hydrogelators reduces the temperature-
induced phase separation of ISAsomes, as shown by the temperature scans on
ISAsome-loaded gel systems in Figure 6.13b. This can be of particular impor-
tance during formulation of more complex systems.
ISAsomes in polymer hydrogels are a fascinating example of structural
hierarchy: LC nanostructures form the internal architecture of submicron-
sized ISAsome particles, which are in turn entrapped in a macromolecular
(polymer) hydrogel network. These systems have some important differences
from the bulk lyotropic mesophases: First, they are still continuous in the
aqueous phase, with a water content of up to 90% or more, but at the same
time they contain a stabilized LC phase inside the ISAsomes. In contrast, bulk
phases cannot hold such high amounts of water. Second, the viscoelastic prop-
erties of bulk phases can only be controlled by changing the temperature and/
or the composition of the LC phase itself, whereas ISAsome-gel systems can
δ
=
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