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Figure 6.6
Stabilization by silica nanoparticles. Cryo-TEM image of ISAsomes with
hexagonal structure stabilized by silica nanoparticles. Block arrows indicate ISAsomes
covered with particulate silica, and the headed arrows show the silica particles in free
or aggregated form in the solution.
6.4 TRANSFER KINETICS OF HYDROPHOBIC MOLECULES IN
MIXED-ISA
SOME
SYSTEMS
Two different ISAsome dispersions—with different nanostructures—can
easily be mixed and equilibrated quite rapidly. In order to understand more
about these interesting equilibration kinetics, various aspects of mixed-
ISAsome systems were studied by Moitzi et al. (2007). Two differently struc-
tured ISAsomes were mixed for this purpose, and the kinetics of structural
transitions was followed using a time-resolved experimental setup on a lab-
based SAXS machine. The nanostructures of the ISAsomes were tuned by
changing the composition of their components [TC and monolinolein (MLO)].
They were followed by using the published phase diagram (Guillot et al.,
2006), which was defi ned by the
δ
value, as given by the formula shown in
(Fig. 6.2 ).
In the simplest example, ISAsomes with H
2
(hexagonal,
δ
=
84) and L
2
(
57) nanostructures were mixed in 1 : 1 proportions; L
2
is also called an
emulsifi ed microemulsion (EME) (Yaghmur et al., 2005). The resulting equili-
brated ISAsomes should have an average composition of
δ
=
70.5, which falls
in the micellar cubic Fd3m region of the phase diagram (Guillot et al., 2006).
This is exactly what was found in the time-resolved SAXS studies, where the
initial phases (H
2
and EME) disappear and Fd3m forms gradually, as shown
in Figure 6.7a. The SAXS signatures for corresponding phases were then fi tted
by a weighted sum of phase fractions (Fig. 6.7b) and were used to quantify the
δ
=
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