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the previous sections in which the scattering curves of the dispersions
corresponded to those of the nondispersed fully hydrated bulk phases.
4 .
Impact of the Stabilizer on the Nanostructure
. The formation of a cubic
Im3m phase in the dispersed MLO-DGMO particles instead of a fully
hydrated nondispersed cubic Pn3m phase was related to the important
role of the stabilizer F127 in the presence of DGMO on the internal
structure after the dispersing process. The same structural transition was
also observed for the aqueous dispersions of a monoolein (MO)-water
system (Larsson, 2000). To illustrate this effect, we explored how the
addition of a small amount of F127 affected the MLO-DGMO bulk
phases. We found that F127 induced the structural transition from the
Pn3m to the Im3m phase (Yaghmur et al., 2006b). In the dispersions, our
results indicated that part of F127 was inserted in the confi ned interior
of the dispersed particles, thus changing the symmetry of the cubic phase
from Pn3m to Im3m, while the other part performed its job as stabilizer
by adhering to the surface of the dispersed particles. This result differed
from our fi ndings described in the previous sections. A possible explana-
tion for this discrepancy might simply be the size of the hydrophilic
channels in these systems: The hydrophilic channels in the binary MLO-
water system were smaller than those in the MLO-DGMO-water or
MO-water system (Yaghmur et al., 2006b). This might be the reason why
the polymer could not be incorporated as easily in the former case.
In order to modify the MLO-based phases, we also investigated partially
replacing MLO by the balanced surfactant PC (Yaghmur et al., 2006b). The
MLO-PC system displayed a different behavior as compared to that of the
MLO-DGMO mixture at the same
ratio: As described in detail in Yaghmur
et al. (2006b), the internal structure contained approximately the same water
content as that of MLO (
β
0). Furthermore, it had a cubic structure of the
Pn3m type, possibly a mixture with Im3m (cubosomes), corresponding well
with the structure of the nondispersed fully hydrated bulk phase with the same
β
β
=
value (data not shown). The result shows that F127 was very effective as a
stabilizer and did not signifi cantly affect the internal nanostructure. However,
the fragmentation of the cubic phases into submicron-sized particles only led
to a lower degree of order (Yaghmur et al., 2006b). Our fi ndings also imply
that the incorporation of the polymer into the lipid bilayers was easier in the
MLO-DGMO mixture than into that of an MLO-PC system.
5.6.2 Tuning Back the Curvature of Oil-Loaded MLO-Based
Aqueous Dispersions
In order to tune back the oil-loaded aqueous dispersions from hexosomes or
EMEs to cubosomes, it is important to replace MLO by a surfactant that has
a countereffect with respect to that of TC. This idea is illustrated in the sche-
matic description presented in Figure 5.14. In Figure 5.15, it can be seen that
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