Hierarchically Organized Systems Based on Liquid Crystalline Phases - Self-Assembled Supramolecular Architectures: Lyotropic Liquid Crystals - page 162

affect the nanostructure at higher surfactant concentrations (Guillot et al.,
2010; Muller et al., 2010a; Sagalowicz et al., 2006c). Moreover, the most com-
monly used triblock copolymer, F-127, can actually penetrate the cubosomes
to some extent and thereby infl uence (disrupt) the structure of at least their
outer shell (Guillot et al., 2006, 2010; Gustafsson et al., 1997). Surfactant sta-
bilizers can be avoided by using solid particles (Cui et al., 2010; Muller et al.,
2010b; Salonen et al., 2008, 2010b); such emulsions are sometimes called
surfactant-free emulsions. The solid particles adsorb onto the surface of so-
called dispersed phase, creating a steric barrier at the interface and stabilizing
the system (Hunter et al., 2008). Such stabilization is well known from the
pioneering work of Ramsden (1903) and Pickering (1907), and the term Pick-
ering emulsions has been established over the years to describe emulsions
stabilized in this manner. In principle, the overall emulsion stability varies
inversely with particle size, as the smaller particles pack more effi ciently,
forming a homogeneous interfacial layer (Hunter et al., 2008). The particle
size ranges from nanometer to micrometer, stabilizing up to millimeter-sized
droplets, which is not commonly observed for surfactant-based systems
(Aveyard et al., 2003). Protein-stabilized food emulsions can also be termed
Pickering emulsions, even though most proteins used for this purpose are also
amphiphilic.
A variety of solid particles are utilized for Pickering emulsions, including
latex particles, metal oxides, carbon and sulfate particles (Dai et al., 2008),
polymeric rods (Noble et al., 2004), grafted polymer brushes (Saigal et al.,
2010), silica (Binks and Lumsdon, 2000), and clay. The latter two are best suited
for stabilizing ISAsomes (Fig. 6.3) because they allow the emulsion stability
to be controlled by changing one or more of the following parameters: charge,
Figure 6.3 Pickering-type nanostructured emulsions. LC nanostructures/phases can
be stabilized as submicron-sized particles by using inorganic solids such as the clay
platelets Laponite and silica nanoparticles. In other words, ISAsomes retain their
original LC nanostructure (from the bulk phase) when stabilized by nanoparticles.
[Figure modifi ed from images in Muller et al. (2010b) and Salonen et al. (2010b).]