Chemistry Reference
In-Depth Information
TABLE 6.1 Effect of Stabilizers F-127 and Laponite on Internal Nanostructure
(Type of LC Phase) and Radius of ISA somes Formed from DU : TC Mixtures
Average Radius of ISAsomes
〈
Internal Nanostructure of ISAsomes
R
〉
(nm)
Laponite —
After 3
Weeks
Laponite —
After 3
Weeks
DU : TC/
Stabilizer
F - 27
Laponite
F - 127
Laponite
100 : 0/0.5
Pn3m
+
Im3m
Pn3m
H
2
116
91
88
90 : 10/0.5
H
2
H
2
H
2
114
93
89
70 : 30/0.5
Fd3m
Fd3m
Fd3m
110
92
88
50 : 50/0.5
L
2
L
2
L
2
99
83
81
Source:
Data taken from Salonen et al. (2008).
angle X-ray scattering (SAXS) pattern of ISAsomes stabilized by 0.5 wt % of
Laponite and with varying internal nanostructure as controlled by the ratio
between lipid (DU) and oil (TC). The stabilization of ISAsomes was found to
differ from that of O/W Pickering emulsions, where stabilization was only
achieved with the addition of salt (Ashby and Binks, 2000). In contrast,
ISAsome stabilization was assisted by the presence of DU and thus did not
require salt addition. This also prevents the development of repulsive interac-
tions between the clay pellets (Salonen et al., 2008).
Laponite clay as a stabilizer for ISAsomes has certain advantages over
F-127. For instance, Laponite does not penetrate the ISAsomes as much as
F-127; in other words, Laponite particles do not change the internal (Pn3m)
nanostructure of cubosomes, in contrast with F127-stabilized ISAsomes (Table
6.1), which have Im3m nanostructure coexisting with the Pn3m. Also, Laponite-
stabilized ISAsomes were smaller than those stabilized by F-127, which indi-
cates that the effective surface area covered per gram of Laponite was higher
than for F - 127.
Laponite has long - term (
3 weeks) effects on the internal structure of
cubosomes made from DU. The Pn3m phase is converted into hexagonal (H
2
)
due to Laponite-induced high pH (pH of 9-10 for
∼
2 wt % Laponite pellets
in water) (Fig. 6.5a). To separate the effect of pH from that of stabilizer type,
a high pH (pH 10) was introduced into the F-127-stabilized ISAsomes. Ini-
tially coexisting Pn3m and Im3m nanostructures (Fig. 6.5c) were transformed
into hexagonal structure within the same period (
<
3 weeks) as shown in
Figure 6.5e. The phase transition can therefore be attributed to the hydrolysis
of ester bonds from the monoglyceride (DU) at high pH (Salonen et al., 2008).
On the other hand, if the H
2
phase transition is desired, this can be achieved
without the use of an external oil additive, as is usually required (Guillot
et al., 2006 ).
Phytantriol, however, was found to be quite stable against such phase transi-
tions (Fig. 6.5b). Interestingly, the lattice parameters of the PT cubic phase
∼
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