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5.2 Emulsified Liquid Crystals and Microemulsions
The stabilized particles described here are based on monolinolein (MLO) +
water mixtures. We aim to determine the role of temperature on their internal
structure; but to understand such systems better, we need to first compare their
internal structure to that of the corresponding bulk. So, the main goal of this
part is to compare the phase transitions in dispersions that are induced by
temperature variations and the behaviour of the nondispersed MLO + water
binary system. Therefore, we determined the phase behaviour in terms of
temperature and composition for the MLO+water system by investigating the
internal structures using SAXS.
The binary phase diagram of MLO + water in Figure 1 comprises a variety
of mesophases depending on temperature and water content. Left of the phase
separation boundary (the thick line) the samples appear macroscopically as
fairly transparent phase (single phase regions), whereas to the right the samples
appear completely white (heterogeneous). In the latter case, the system sepa-
rates into the mesophase and excess water. In this system, the bicontinuous
cubic mesophase Pn3m can contain considerably more water than the reverse
hexagonal phase H
2
or the L
2
phase formed at higher temperatures. At 201C
the MLO can solubilize up to 33 wt.% water, whereas at 941C it can solubilize
100
L
2
+ water
L
2
H
2
+ water
80
H
2
60
40
Pn3m + water
Ia3d
Pn3m
L
α
20
0
10
20
30
40
water content [%wt]
Figure 1 Temperature-composition phase diagram of MLO + water determined by
SAXS in the heating direction. The lines are guides for the eye to see the phase
transitions and the regions of coexistence between the mesophases. The thick
line corresponds to the phase separation boundary between the single-phase
regions (left) and the excess water region (right)
(Schematic representations reprinted with permission from Refs. 17,18.)
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