Chemistry Reference
In-Depth Information
high-energy dispersion, such as, homogenization and ultrasonication, to low-
energy dilution from precursor formulation with additives such as ethanol. The
choice of dispersion technique is based on the requirements for the particular
application. Less destructive methods such as dilution may be required for
the incorporation of sensitive molecules, while high-energy techniques may
provide more uniform crystalline structure.
The materials used for the formation of LCNP are categorized into two
parts: the lipids that assemble into the nanostructure and the stabilizer that
stabilizes the dispersion. It is crucial to choose a lipid system that can form
stable reversed phases (cubic, hexagonal, or sponge) in excess of solvent. For
example, one of the most widely studied lipid system is the glycerol mono-
oleate (GMO)-water system. GMO forms reversed bicontinuous cubic phase
in equilibrium with excess water and is commercially available as a food emul-
sifi er (Boyd et al., 2009; Larsson 1989, 1991; Sagalowicz et al., 2006a). To dis-
perse the crystalline phases into particulate form, it is essential to locate a
suitable dispersion stabilizer for the particular lipid system. A dispersion sta-
bilizer is needed to reduce the exposure of the hydrophobic domains to
aqueous medium, that is, reduce the interfacial tension, and to prevent aggre-
gation of the dispersed particles, which apart from forming large aggregates
can also lead to the disruption of the inner crystalline structure. The stabilizer
should not interfere with the crystalline phases and at the same time provide
stability to particle formation. To satisfy these requirements, a stabilizer is
typically amphiphilic with a hydrophobic region that is (partly) miscible with
the particular lipid, and hydrophilic unit(s) at the surface of the particle
provide steric repulsion against aggregation. One of the most effective and
commonly used stabilizers, which works well with GMO, is a block copolymer
called Pluronic F-127 (Barauskas et al., 2005b; Boyd et al., 2009; Landh, 1994).
Pluronic has a hydrophobic block, polypropylene oxide (PPO), which is sand-
wiched between two hydrophilic polyethylene glycol (PEO) chains. The PEO
chains cover the surface of the nanoparticle and dominate the interfacial
interaction. In order to control the interfacial properties of LCNP, it is crucial
to understand the properties and surface interaction of the stabilizer because
this will control the interfacial behavior of LCNP.
10.3
CHARACTERIZATION TECHNIQUES
A range of techniques are available to study the properties of LCNP. For this
review, we focus on those that probe the LCNP behavior at the solid-water
interface, such as neutron refl ectometry, null ellipsometry, quartz crystal micro-
balance, fl orescence microscopy, and Fourier transform infrared spectroscopy.
These methods are particularly advantageous to use as they are nonperturba-
tive techniques that are very sensitive to the interfacial properties, thus allow-
ing for the structural and/or compositional information at the surface layer to
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