Self-Assembly in Lipidic Particles - Self-Assembled Supramolecular Architectures: Lyotropic Liquid Crystals - page 130

This chapter describes the effect of variations in temperature and solu-
bilizing oil on the reversible structural transitions of the nanoscale interior
self-assembled domains of the kinetically stabilized MLO-based droplets.
Intriguingly, our fi ndings demonstrated that the formation of the confi ned
nanoscaled tunable hierarchical structures was driven only by the principles
of self-assembly. Our results revealed the possibility to emulsify W/O micro-
emulsion systems—even at room temperature—by adding an oil such as
tetradecane (TC) to the binary MLO-water system. The formed interior
nanostructures were thermodynamic equilibrium structures, and the emulsi-
fi ed particles showed a swelling-deswelling behavior during the heating/
cooling cycles (denoted as “breathing mode”). We also demonstrated that the
interior self-assembled nanostructures of these dispersed droplets could be
modulated by varying the lipid composition (Yaghmur et al., 2006b). This
could be achieved by replacing a certain amount of MLO by a surfactant
favoring the formation of the L α structure. For instance, we found that diglyc-
erol monooleate (DGMO, a nonionic polar lipid with a large headgroup) had
a signifi cant impact on the internal nanostructures of MLO-based aqueous
dispersions (Yaghmur et al., 2006b).
Our main concern was to prove that both the oil-loaded and the oil-free
self-assembled nanostructures were preserved in the presence of the stabilizer
after application of a high-energy input during the dispersing procedure. To
achieve this objective, it was important to carry out detailed systematic inves-
tigations on both the dispersed and the nondispersed bulk phases. In this
chapter, we describe also the temperature - induced direct liposomes - cubosomes
transitions in the binary monoelaidin (ME)-water system.
The interested reader is also directed to the contribution of Glatter and
Kulkarni (Chapter 6) in this topic. They summarized further recent studies on
these nanostructured aqueous dispersions.

5.2 EMULSIFICATION OF MLO-WATER NANOSTRUCTURES

Various studies have been performed to prepare stable lipidic colloidal disper-
sions of V 2 and H 2 phases, and subsequently explore their internal structure
(Angelova et al., 2005; Barauskas et al., 2005; Gustafsson et al., 1996; Larsson,
2000; Rizwan et al., 2007; Spicer, 2004). This section describes investigations
devoted mainly to characterizing the temperature-induced structural transi-
tions of the various confi ned nanostructures in the dispersions in order to
explore the temperature-dependent reversible formation of self-assembled
internal structures, as well as to report on the formation of what we termed
an emulsifi ed L 2 phase (ELP) at high temperatures.
In order to shed light on the confi ned nanostructure of the MLO-water
system in a colloidal emulsifi ed state, MLO was dispersed in large amounts of
excess water by means of ultrasonication, where the block copolymer F127
was used as stabilizer. This led to the formation of submicron-sized cubosome