Chemistry Reference
In-Depth Information
The formation of EMEs is very attractive in both basic and applied research
since these unique nanostructured droplets have superior physicochemical
properties to conventional emulsions and double emulsions. These effective
nanoparticulate systems are of great interest for various pharmaceutical,
food, and cosmetic applications.
Our study revealed that the addition of TC increased the fl exibility of the
surfactant fi lm, thereby destabilizing the internal H
2
phase in favor of an
inverted microemulsion phase. It was thus evident that it was possible for the
formation of droplets confi ning W/O microemulsion system at room tempera-
ture to take place (Yaghmur et al., 2005).
Our results also indicate that the structural transformation from hexosomes
to EME was not direct but rather took place in a certain TC concentration
range in which micellar cubosomes with the internal space group Fd3m (also
referred to by the symbol I
2
) were formed between the hexosomes and EMEs.
However in the absence of TC (Fig. 5.1), the results with respect to both the
dispersed and the nondispersed systems were similar to those from other previ-
ous investigations carried out on the impact of temperature on the phase
behavior of binary monoglycerides-water systems (Barauskas & Landh, 2003;
de Campo et al., 2004; Larsson, 1983; Lindblom et al., 1979; Lutton, 1965; Qiu &
Caffrey, 1998, 1999): None of these studies displayed any indication of the exis-
tence of the Fd3m phase when the temperature was varied from 20 to 94°C.
It was important to prove that confi ned oil - loaded self - assembled nano-
structures could be well preserved during the formation of the emulsions. We
also wished to show that there was no
leaking
process in the internal nano-
structure, which could occur as a result of either TC or water being expelled
from these structures to the surrounding aqueous phase. Our approach was to
simply compare the structural transitions of the TC-loaded dispersed MLO
particles to those that occurred in the corresponding fully hydrated nondis-
persed ternary MLO-TC-water systems. It is also noteworthy that the addi-
tion of TC decreased the water solubilization capacity. For instance, in the
absence of oil (
0), the water content was determined to be approximately
32 wt % (de Campo et al., 2004). Upon increasing the TC content to
α
=
19,
75, and 110, the water content decreased to less than 25, 20, and 15 wt %,
respectively (Yaghmur et al., 2005).
We found in all investigated dispersions (of which two examples are pre-
sented in Fig. 5.6) that the internal structures were well preserved: The peak
positions were identical to those of the corresponding nondispersed fully
hydrated samples. Figure 5.6a shows an oil-loaded H
2
phase, and Figure 5.6b
displays an example of an EME with an internal nanostructure identical to
that of the corresponding nondispersed W/O microemulsion coexisting with
excess water (Winsor-II-type microemulsion system). We were thus, in princi-
ple, able to form EMEs without concomitant loss of the W/O microemulsion's
integrity. The average hydrodynamic radius of these droplets, as determined by
dynamic light scattering (DLS), was in the range of 120-200 nm.
The submicron-sized dispersed EME particles were also observed by cryo-
TEM. Figure 5.7 shows that the confi ned W/O nanostructures were clearly
α
=
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